RPM's Jump After Cleaning Throttle Body

jason43080

Original poster
Member
Jun 20, 2012
42
Birmingham
Hello everyone, I will try try to make this as short as possible. I cleaned my throttle body a few months ago on my 08' TrailBlazer after I bought it. The first time I didn't disconnect the battery like I should have before cleaning it, I left it on and sprayed the butterfly and the inside. The next day I noticed the RPMs would jump and dip a bit but ONLY when I was coasting, never at a complete stop or while accelerating. A few weeks later I cleaned it again but this time I removed the TB and disconnected the battery first, next day same problem. It's been approximately 2 months now and a mechanic friend of mine told me it needed an idle relearn so I took it to the shop today and had it done. They cleaned the MAF sensor and did a few other things to it as well. Anyway, my RPMs still do the jump and dip even after taking it to the shop, no change. I took it to another shop and they said that since the TB is controlled by the computer, by me manually opening the the butterfly when cleaning it, it has gotten it out of sync. They told me my options are to take it to a Chevy dealership and have the system flashed($$) or replace the throttle body itself($$$$). Does this sound right to you guys, does anyone have experience with this issue as well? Thanks for any and all advice and suggestions!
 

Wooluf1952

Member
Nov 20, 2011
2,663
Milwaukee, Wisconsin
Manually opening the butterfly should only harm the t-body if you had the key in the ON position.

When you cleaned the t-body, did you take it off to clean the inside?

Usually just spraying cleaner doesn't do it. It needs to be scrubbed.

Do the RPM's always jump? Or just when the AC or Defroster is ON?
 

The_Roadie

Lifetime VIP Donor
Member
Nov 19, 2011
9,957
Portland, OR
If you push on the butterfly valve with the ignition on and the battery connected, you can burn out a stepper motor. If it was powered off, the mechanic is lying or confused.

Does the idle stabilize if you force the AC system off?

When it jumps, is it when the AC compressor clutch cycles on and off (observe it)?

How many RPM does it move when it goes up and down? How often between highs and lows?

Might be a sluggish CPAS, is the next most likely thing IMHO.

How many miles, and if over 100K, are the plugs new? How about ALL fluids? How old?
 

CaptainXL

Member
Dec 4, 2011
2,445
jason43080 said:
does anyone have experience with this issue as well? Thanks for any and all advice and suggestions!

I had something similar happen to my truck. I had to disconnect the battery overnight. I read somewhere that the throttle angle memory won't clear as fast so i just tried it. You might also want to look into cleaning the orifice for crankcase blowby. I have never done it but it is something new to me and will be investigating soon. The orifice is at the drivers side of the intake manifold. There is a big L shaped hose.
 

jason43080

Original poster
Member
Jun 20, 2012
42
Birmingham
Thanks for the fast response guys! The first time I didn't remove the TB, I just sprayed it down with cleaner on the inside and out, by pushing open the butterfly with my fingers. The second time I removed the TB and disconnected the battery for an hour or so before taking it for a spin. Neither time were the keys in the ignition. It happens whether the AC is running or not, it doesn't seem to be time or temperature related either. My longest trip so far with the car has been roughly a 40 minute drive one way, it did it from begining to end of the trip. It only does it when coasting, not when at a stop or accelerating. It appears to jump up about one click and then dips down 4 clicks and then jumps back up to normal RPMs(what it was out before it started jumping). It's an 08' with 85K on it, 2 shops have inspected it and said everything looks to be in great shape, fluids, belts, etc. I bought the car used from CarMax back in April so I'm not sure about previous maintenance that was done on it before hand. When I bought the car it wasn't doing it, it was only after I cleaned the TB that all this started. I was extra careful and have done this a few time on my 04' TrailBlazer before it was wrecked.
 

jason43080

Original poster
Member
Jun 20, 2012
42
Birmingham
Thanks for the suggestion Captain, I just unplugged the battery and will leave it unplugged until I head to work tomorrow afternoon! I have tried disconnecting the battery a few times but about an hour was the longest I have let it sit.
 

TexazReece

Member
Dec 4, 2011
1,341
Man I hope leaving the battery disconnected until tomorrow works. I will def make sure I disconnect the battery when doing this Good Luck bro
 

jason43080

Original poster
Member
Jun 20, 2012
42
Birmingham
Thanks Texaz, me too, either of my other options of having it reflashed or replacing the TB will cost way more money than I'm looking to spend on this right now, hopefully this will work.
 

CaptainXL

Member
Dec 4, 2011
2,445
jason43080 said:
Thanks Texaz, me too, either of my other options of having it reflashed or replacing the TB will cost way more money than I'm looking to spend on this right now, hopefully this will work.

You are only seeing a slight dip when coasting and no issues at all when accelerating or stopped. Without looking at it this could be considered normal given the way our PCM's are programmed. Unless you have mileage issues or some safety issue I wouldn't take such drastic measures.

If you had an issue with the Throttle Body then the computer would flash a Check Engine Light. The computer uses the Pedal Position Sensor and compares its data against the built in Throttle Position Sensor. If there are any discrepancies it will let you know.

My suggestion would be to look elsewhere if the battery disconnect doesn't solve the issue. For instance... check engine vacuum and fuel trims while coasting.

If you decide to replace the throttle body and it fixes your issue then please let us know.
 

jason43080

Original poster
Member
Jun 20, 2012
42
Birmingham
I don't think this is normal operation as the vehicle didn't do this before I cleaned the TB. I know there where some changes from 04' to 08' but my 04' never had this issue. It does seem to be something related to the TB opening and closing properly though. When I let off the pedal, instead of the RPMs dropping immediately, it stays where it's at anywhere from 4 to 8 seconds before it drops. There have been no engine lights or codes thrown thus far. It could be a bad vacuum hose or sensor as others have stated but it seems ironic to me that a hose or sensor would go bad or start leaking the day after cleaning the TB. I will see if disconnecting the battery over night fixed the problem or not this afternoon and report back here. Again, thanks so much for your help and suggestions guys, I really appreciate you all, this is a great site with friendly, helpful people!
 

SAR85

Member
Jan 31, 2012
74
When you removed the intake resonator to remove the throttle body you had to disconnect the PCV hose. Did you make sure to reconnect it? That could be a cause of vacuum leak related to the procedure.
 

jason43080

Original poster
Member
Jun 20, 2012
42
Birmingham
SAR, I'm so glad you posted your question, when I cleaned the TB I made sure everything was reconnected as before, I triple checked it. When I saw your post I went to check the connections again and apparently yesterday one of the shops didn't reattach the hose on the bottom of the resonator. Even if disconnecting the battery works, not having all hoses attached could have made it continue to malfunction. I'm heading to work in about an hour, thanks to you, I have confirmed all hoses have been properly reattached. I should have double checked that yesterday when I got home but I had really busy day yesterday, thank you for posting!
 

Wooluf1952

Member
Nov 20, 2011
2,663
Milwaukee, Wisconsin
jason43080 said:
SAR, I'm so glad you posted your question, when I cleaned the TB I made sure everything was reconnected as before, I triple checked it. When I saw your post I went to check the connections again and apparently yesterday one of the shops didn't reattach the hose on the bottom of the resonator. Even if disconnecting the battery works, not having all hoses attached could have made it continue to malfunction. I'm heading to work in about an hour, thanks to you, I have confirmed all hoses have been properly reattached. I should have double checked that yesterday when I got home but I had really busy day yesterday, thank you for posting!

You should not have to check the work of a shop. Too bad you don't know which shop screwed-up for future reference.
 

jason43080

Original poster
Member
Jun 20, 2012
42
Birmingham
I agree with you Wooluf, you shouldn't have to double check the work of a shop. I really can't complain too much though, the first shop gave me an oil change(with synthetic), idle relearn, and spent a few hours researching the issue for $40 because a referral of a friend. The second shop had 6 different mechanics look at it and ran a can of intake cleaner through the engine, cleaned the MAF sensor, and ran other diagnostic stuff on my car for absolutely free. Besides forgetting to reattach the hose, both shops really hooked me up big time.

My latest update: I drove about 25 miles to work this afternoon and no issues this time, RPMs held steady, no funny business. My drive is 1/2 city and 1/2 interstate and it ran perfectly on the way there and the way back. I will give it a few days before I feel certain the issues fixed but I was pleasantly surprised with the results of leaving the battery disconnected over night! Thank you everyone that has posted and helped me with the issue and a BIG thank you to CaptainXL, I will keep you all posted!
 

MacMan

Member
Mar 3, 2012
194
jason43080 said:
My latest update: I drove about 25 miles to work this afternoon and no issues this time, RPMs held steady, no funny business. ............ I was pleasantly surprised with the results of leaving the battery disconnected over night!

I'm guessing the disconnected hose caused the high idle (lean mixture....like having the throttle opened a little).

In the future, 45-60 minutes of battery disconnect is PLENTY.

Glad you got it straightened out <fingers crossed>.
 

jason43080

Original poster
Member
Jun 20, 2012
42
Birmingham
Thanks for the well wishes MacMan, I really appreciate it. My understanding was that 60 minutes was all that was needed for the system to fully reset but I had tried that the first few time and all hoses were connected then. Who knows, it could have been the idle relearn or something else one of the shops did that in theory fixed it? I'm still a bit skeptical that it will continue working properly but I'm being optimistic. I will continue to post if the issue arises again but hopefully in a few days I can report problem solved!
 

jason43080

Original poster
Member
Jun 20, 2012
42
Birmingham
Okay, so I was taking my girlfriend to work this morning and as soon as we left...you guessed it, the RPMs start jumping again. It did it the whole trip there and back, same thing, only while coasting. I am not a mechanic nor am I an expert when it comes to our vehicles but if it ran perfectly all day the day before I don't think it would be a leak in a hose somewhere. It would seem that the computer is telling the TB to open and close etc at the wrong time. This may be the system still relearning from the battery disconnect and I will give it more time to see if it works itself out, I just wanted to give an update on the situation.
 

jason43080

Original poster
Member
Jun 20, 2012
42
Birmingham
Well it's been a few days since I last posted and I am still having the RPMs jump after taking to two shops and leaving the battery disconnected over night. Any ideas or suggestion guys, I'm really stumped on this one and would love to have the issues fixed? Thanks again for all your help!
 

jason43080

Original poster
Member
Jun 20, 2012
42
Birmingham
Thanks for the response Strat, I'm open to suggestions. How could I test for inadequate/unstable fuel pressure, I'm not sure if that's the issues but I would like to rule it out if it's not. A few days before I cleaned the TB I ran some Lucas cleaner through the system and the next tank ran some Techron. I doubt that would have an effect on the issue but it might. Maybe semi-clogged fuel filter, would that cause the issues or would that cause it to jump while accelerating and when stopped as well?
 

strat81

Member
Dec 29, 2011
399
jason43080 said:
Thanks for the response Strat, I'm open to suggestions. How could I test for inadequate/unstable fuel pressure, I'm not sure if that's the issues but I would like to rule it out if it's not. A few days before I cleaned the TB I ran some Lucas cleaner through the system and the next tank ran some Techron. I doubt that would have an effect on the issue but it might. Maybe semi-clogged fuel filter, would that cause the issues or would that cause it to jump while accelerating and when stopped as well?

Amazon.com: Actron CP7838 Professional Fuel Pressure Tester: Automotive

The long hose on that model is nice because you can attach the valve to the fuel rail, tape the gauge to your windshield, and take the vehicle for a drive. Have a friend watch the gauge to see if it shows erratic pressure while driving.

Regarding fuel additives, based on some reading at BobIsTheOilGuy.com, there are very few that actually do anything. You can read up and draw your own conclusions. Even the lousy ones shouldn't really hurt anything though.

Your fuel filter is part of the fuel filter assembly inside the tank. I suppose it could be clogged, but I'm told the filters are very large and are designed to last for the life of the vehicle (or at least the pump) under most conditions. Unless someone is dumping sand in your tank, that may not be the issue.

How many miles are on your current fuel pump?


If you had an older or different vehicle, I'd say that it might be the fuel pressure regulator, but IIRC, 2008 TBs do not have them (or, rather, it's part of the pump assembly). Do some reading on returnless fuel injection systems.
 

jason43080

Original poster
Member
Jun 20, 2012
42
Birmingham
Thanks for the info guys, I will look into getting one of those and see if that may be the issue! I don't believe that any of the fuel additives are a "Miracle in a bottle" as some claim, but I do think they can help loosen deposits and aid a bit in cleaning the fuel system. I don't use them religiously but I did add some after I got the car because I had no idea the condition of the system or what brand of gas had been regularly used. I stick with Chevron or Shell for the most part, it's worth a few extra cents to me to use top tier gas rather than the bargain stuff. I'm not sure how many miles are on the fuel pump, I bought the car from CarMax back in April of this year so I don't know what all has been replaced since they got the car. Maybe it was the older ones(02-05) but I thought the fuel filter was under the passenger side of the car, not in the tank, and could be replaced?
 

The_Roadie

Lifetime VIP Donor
Member
Nov 19, 2011
9,957
Portland, OR
jason43080 said:
...Maybe it was the older ones(02-05) but I thought the fuel filter was under the passenger side of the car, not in the tank, and could be replaced?
It was the older ones that were easily replaceable. New ones are in the tank, and need no service. (The fuel level sensor or the pump will die first, trust me. :wink: )
 

SAR85

Member
Jan 31, 2012
74
Since I seem to be in the habit of suggesting to check for disconnected hoses...did you also make sure to reattach the fuel pressure regulator vacuum line when putting everything back together?
 

CaptainXL

Member
Dec 4, 2011
2,445
I keep reading in other forums that it is neccessary to calibrate the throttle body by turning the ignition on and let it sit for about 10 minutes. Not sure if that goes along with our system but i read that motorola based fuel injection systems do that. I did it today after replacing my ignition switch.
 

jason43080

Original poster
Member
Jun 20, 2012
42
Birmingham
I'm not sure which hose that is SAR, could you point me in the right direction please? Thanks for the info Captain, after I cleaned the TB the first time, I let it run for about 20-30 minutes to burn off the excess spray, didn't seem to work, the day after was when all this started.
 

CaptainXL

Member
Dec 4, 2011
2,445
jason43080 said:
I'm not sure which hose that is SAR, could you point me in the right direction please? Thanks for the info Captain, after I cleaned the TB the first time, I let it run for about 20-30 minutes to burn off the excess spray, didn't seem to work, the day after was when all this started.

No. not what I said. Turn the key on but do not start it. After 5 or more minutes turn the key off.
 

SAR85

Member
Jan 31, 2012
74
jason43080 said:
I'm not sure which hose that is SAR, could you point me in the right direction please? Thanks for the info Captain, after I cleaned the TB the first time, I let it run for about 20-30 minutes to burn off the excess spray, didn't seem to work, the day after was when all this started.

The hose is on the driver side of the intake resonator.
 

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CaptainXL

Member
Dec 4, 2011
2,445
SAR85 said:
The hose is on the driver side of the intake resonator.

The fpr is integral to the intank fuel pump from 2005 onward. Its a returnless system so those vehicles dont have that hose.
 

jason43080

Original poster
Member
Jun 20, 2012
42
Birmingham
Thanks for uploading the pics SAR, it really helped me understand what you were talking about but Captain is correct, mine doesn't have that hose. I took your advice Captain, I turned the key all the way forward and listened to some tunes for about ten minutes and then turned it off, I will see if there is any difference tomorrow and report back.
 

CaptainXL

Member
Dec 4, 2011
2,445
jason43080 said:
Thanks for uploading the pics SAR, it really helped me understand what you were talking about but Captain is correct, mine doesn't have that hose. I took your advice Captain, I turned the key all the way forward and listened to some tunes for about ten minutes and then turned it off, I will see if there is any difference tomorrow and report back.

I forgot to mention that you aren't supposed to press any pedals. If you did even a little bit you need to start over. I know. It's kind of weird leaving the keys in your car like that without touching anything. Just leave the door ajar so you don't lock yourself out. Don't use the fob.

I noticed my acceleration was much smoother today. Looks like it did something but can't be 100% certain I guess.
 

jason43080

Original poster
Member
Jun 20, 2012
42
Birmingham
Very interesting, as long as I don't have to hold my breathe and hop up and down on one leg during the process, I will try it, I have nothing to lose right?
 

CaptainXL

Member
Dec 4, 2011
2,445
jason43080 said:
Very interesting, as long as I don't have to hold my breathe and hop up and down on one leg during the process, I will try it, I have nothing to lose right?

Oh one more thing. Make sure you sacrafice a chicken and pray to Mars before you....haha
 

jason43080

Original poster
Member
Jun 20, 2012
42
Birmingham
I am out of chickens so a frozen steak will have to suffice, Mars better be impressed! I thought it was the blue wire Wooluf, back to the drawing board! Did you crank it or take it for a spin after the process or "in theory" when I crank it up and head to work in the morning it should be calibrated?
 

CaptainXL

Member
Dec 4, 2011
2,445
jason43080 said:
I am out of chickens so a frozen steak will have to suffice, Mars better be impressed! I thought it was the blue wire Wooluf, back to the drawing board! Did you crank it or take it for a spin after the process or "in theory" when I crank it up and head to work in the morning it should be calibrated?

When done waiting the right amount of time you turn it off and take the key out to be sure. Then fire it up and go. Lets see how it goes.
 

jason43080

Original poster
Member
Jun 20, 2012
42
Birmingham
Gottcha, well I did it and let it sit for ten minutes, this time I didn't touch anything! It's too late to take it for a spin but I will see how it does on the way to work tomorrow and if no change, I will do the process again and then take it for a drive after. Thanks for the info by the way, you guys are most appreciated!
 

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