Idle RPM surged then hung at 1K ?

Mypetropig

Original poster
Member
Dec 29, 2011
226
First time calling for help on this site, any advice is welcome.Coming to a stop light today and once stopped the idle surges back and forth from normal to 1k and dropped below 600 a couple of times but never stalled. When I came to the next light the idle was hanging around 950-1K. The idle stayed this high until I got home and turned it off. It gave no CEL and had no reduction in power. After the truck sat a while I tried to investigate. I started it and the idle settled around 1k as if this was normal. I removed the resonator at the TB and noticed the butterfly was open alot more than it should be, I could push it in about a 1/2 inch. I didnt see anything obvious so I just disconnected the battery for a while and put it all back togther. After about 20mins I started the truck and all is fine. My question is could this be a throttle body or a component of it going bad?

Recent maintenance :

Mileage is approx 102k
Brakes and brake fluid flush about 500 miles ago
Oil change, Air filter and throttle body cleaning, fuel filter replaced 800 miles ago ( yes the battery was disconnected )
Plugs were changed at about 80k
Intake manifold was cleaned with Seafoam (aerosol w/30" straw) approx 800 miles ago
MAP sensor in intake recently cleaned

:helpme:
 

RayVoy

Member
Nov 20, 2011
939
I would start with a throttle body cleaning. A search will uncover a ream of info
 

MacMan

Member
Mar 3, 2012
194
RayVoy said:
I would start with a throttle body cleaning. A search will uncover a ream of info

He did that already.
 

Simon01

Member
Dec 5, 2011
116
Is it possible that the PCV lines weren't installed tightly when you did the TB service, and when you checked the TB today you fixed it after putting the resonator back on?
 

MMIN

Member
Feb 26, 2012
55
Unfortunately at this point could be a lot of different things.. I'll throw out that it could be one of the coil packs going bad.. They start off that way as well but take a while to throw a CEL. Did it rain recently? Pop a few out and see if any cylinders are full of water.
 

Mypetropig

Original poster
Member
Dec 29, 2011
226
Simon01 said:
Is it possible that the PCV lines weren't installed tightly when you did the TB service, and when you checked the TB today you fixed it after putting the resonator back on?

I guess it was possible, do you think that should have shown up sooner?

MMIN said:
Unfortunately at this point could be a lot of different things.. I'll throw out that it could be one of the coil packs going bad.. They start off that way as well but take a while to throw a CEL. Did it rain recently? Pop a few out and see if any cylinders are full of water.

It has rained recently but the truck was not driven in it, it was tucked neatly away in the garage. Its worth checking out though. No problems since disconnecting the battery.
 

The_Roadie

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Nov 19, 2011
9,957
Portland, OR
Mypetropig said:
...noticed the butterfly was open alot more than it should be, I could push it in about a 1/2 inch. ...
No matter what else you find - NEVER push on the butterfly valve if the power is on and the PCM is controlling its position. You'll be fighting the stepper motor inthe throttle body and can burn it out. A common warning for all electronic systems like ours.

Check the fuel pressure regulator vacuum hose to the intake manifold. If it falls off, RPMs go to 900 and it doesn't throw a code for a while. And the mixture is messed up due to the vacuum leak.
 

Mypetropig

Original poster
Member
Dec 29, 2011
226
When I applied pressure to the butterfly the truck was off, I checked the hose for the fuel pressure regulator first. I can pull it off and notice no change in the RPM's. Today it messed up again while my wife was parking in the garage. Her foot was on the brake, shifter in park and set the parking brake. She said the RPM's stumbled and went to 1K then slowly dropped down to about 450-500 then it died. It started back with out hesitation and has been driven since with no problems or CEL's yet. Is there a way to test the coil packs or do I have to hope for a CEL since I dont have a scan tool or smart phone with the torque app.
 

Mypetropig

Original poster
Member
Dec 29, 2011
226
:bump:

I am going to test the coil packs with a volt meter then pull them and check for any water. Since the packs will be out I will pull the plugs to check them, also check /clean the cam position actuator solenoid. I noticed that it is weeping a little oil at the connector. The truck has been running fine the past couple of days, go figure :weird:. I am thinking about replacing the coil boots if I don't find any thing else.
 

Mypetropig

Original poster
Member
Dec 29, 2011
226
CaptainXL said:
Did you just buy this truck? How many miles ago?

We have had this truck for 4yrs and it had approx 68k on it then. We got the truck from our mother in law who past away, it has a little over 102k on it now.
 

CaptainXL

Member
Dec 4, 2011
2,445
Mypetropig said:
We have had this truck for 4yrs and it had approx 68k on it then. We got the truck from our mother in law who past away, it has a little over 102k on it now.

Did you remove the throttle body and clean both sides?
 

Mypetropig

Original poster
Member
Dec 29, 2011
226
CaptainXL said:
Did you remove the throttle body and clean both sides?

Yes I removed it and cleaned both sides as well as disconnected the battery. I was a member of the other site for several years, I learned a lot from the gurus there and have followed them here.
 

Mypetropig

Original poster
Member
Dec 29, 2011
226
I am not sure if it was done before we got the truck. I plan on doing it in the next week or so. I checked the coils with a meter today and they are fine. The plugs are good, only about 25k on them. I found no water in the coil pack cavities and cleaned the connector for the CPAS because it was weeping a little oil. I also replaced the throttle body gasket as it had become compressed, it was only about $5 so what the heck.
 

CaptainXL

Member
Dec 4, 2011
2,445
Mypetropig said:
I am not sure if it was done before we got the truck. I plan on doing it in the next week or so. I checked the coils with a meter today and they are fine. The plugs are good, only about 25k on them. I found no water in the coil pack cavities and cleaned the connector for the CPAS because it was weeping a little oil. I also replaced the throttle body gasket as it had become compressed, it was only about $5 so what the heck.


Sounds like you found the problem. Vacuum leak. You need a new CPAS as well.
 

Mypetropig

Original poster
Member
Dec 29, 2011
226
Can anybody confirm if 12615873 is the current part number for the CPAS? gmpartsshop lists it as a valve, gmpartsdirect lists it as a camshaft sensor for Colorado/Canyon and rockauto does not list it at all.
 

MacMan

Member
Mar 3, 2012
194
Mypetropig said:
Can anybody confirm if 12615873 is the current part number for the CPAS? gmpartsshop lists it as a valve, gmpartsdirect lists it as a camshaft sensor for Colorado/Canyon and rockauto does not list it at all.

Yes, that is correct.

Use Google Product Search for info on buying parts for most anything. Just input the part # at the top.
 

Mypetropig

Original poster
Member
Dec 29, 2011
226
MacMan said:
Yes, that is correct.

Use Google Product Search for info on buying parts for most anything. Just input the part # at the top.

Thanks for the confirmation and the link for info.
 

bastenblood

Member
Dec 22, 2011
23
A few months ago my envoy had the same problem . I were driving in the snow and stopped at a red light , the rpm
suddenly goes up to 900 rpm and the engine light came on too , after a few minutes things were back to normal ,
and this happened a few times .

So the problem was the manifold oxygen sensor , cost me 75$ for a new one and never had any problem since .
 

Mypetropig

Original poster
Member
Dec 29, 2011
226
Just as I thought we were in the clear on this stalling thing, it happened again.:banghead: Tonight as my wife was coming to a stop it surged for a second and stalled. No CEL or anything and it fired right up and ran fine for the rest of her errands. Strange thing is she says that now cruise control does not work. I recently replaced the brakes all around and bled /flushed the fluid, would there be anything related causing a drop in vaccum or something? It seems to only happen when stopped or coming to a stop is the reason I ask.:helpme:
 

CaptainXL

Member
Dec 4, 2011
2,445
Mypetropig said:
Just as I thought we were in the clear on this stalling thing, it happened again.:banghead: Tonight as my wife was coming to a stop it surged for a second and stalled. No CEL or anything and it fired right up and ran fine for the rest of her errands. Strange thing is she says that now cruise control does not work. I recently replaced the brakes all around and bled /flushed the fluid, would there be anything related causing a drop in vaccum or something? It seems to only happen when stopped or coming to a stop is the reason I ask.:helpme:

I would get the STFT fuel trim looked at. Also just because the CEL isn't on doesn't mean you don't have any pending codes or misfire data. Get it scanned.
 

Mypetropig

Original poster
Member
Dec 29, 2011
226
CaptainXL said:
I would get the STFT fuel trim looked at. Also just because the CEL isn't on doesn't mean you don't have any pending codes or misfire data. Get it scanned.

I will get it scanned asap. Does STFT mean short term fuel trim?
 

Mypetropig

Original poster
Member
Dec 29, 2011
226
Tonight the engine did not stumble at all but I noticed that the RPM's are stuck at about 900. Could it be a bad MAF sensor or a bad CPAS? I don't recall if I mentioned this in previous post but the plugs and the o2 sensor in the manifold have about 25k on them and yes they are both AC-Delco. I friend of mine has a scan tool but cant get to it until next weekend. Other than STFT and fuel pressure what should we be looking for? Will we be able to get useful info if the truck is not screwing up on that day?
 

CaptainXL

Member
Dec 4, 2011
2,445
Mypetropig said:
Tonight the engine did not stumble at all but I noticed that the RPM's are stuck at about 900. Could it be a bad MAF sensor or a bad CPAS? I don't recall if I mentioned this in previous post but the plugs and the o2 sensor in the manifold have about 25k on them and yes they are both AC-Delco. I friend of mine has a scan tool but cant get to it until next weekend. Other than STFT and fuel pressure what should we be looking for? Will we be able to get useful info if the truck is not screwing up on that day?

I would disconnect the battery for about an hour and then see what you get.
 

recondrill

Member
Jan 8, 2012
5
Change MAP sensor ($35) and replace O2 sensors. With everything else you've done, this should help. I had the same problem with a bad idle and after changing the MAP sensor, all seems fixed. Double check for vaccum leaks with some carb cleaner and spray all vaccum connctions. Don't forget about the brake booster line and against the pass side fire wall.
 

Mypetropig

Original poster
Member
Dec 29, 2011
226
CaptainXL said:
I would disconnect the battery for about an hour and then see what you get.

If I do this it resets everything and it seems fine for a few days.

recondrill said:
Change MAP sensor ($35) and replace O2 sensors. With everything else you've done, this should help. I had the same problem with a bad idle and after changing the MAP sensor, all seems fixed. Double check for vaccum leaks with some carb cleaner and spray all vaccum connctions. Don't forget about the brake booster line and against the pass side fire wall.

I thought about changing the MAF sensor and was looking at pricing last night along with the IAT sensor. My friend with the scan tool mentioned the carb cleaner trick and I am going to try that asap. What symptoms would a failing CPAS give?
 

CaptainXL

Member
Dec 4, 2011
2,445
Mypetropig said:
If I do this it resets everything and it seems fine for a few days.

A good scan tool will show you if all of the Readiness tests have been completed. If you don't get a CEL then I assume they all passed. But it doesn't hurt to check.
 

CaptainXL

Member
Dec 4, 2011
2,445
Mypetropig said:
What symptoms would a failing CPAS give?

From what I gather its poor performance and bad gas mileage in the city. Also occasional backfiring if cam does not advance while accelerating. Unplug the CPAS and see if you notice a difference. Since you have a 2003 it's probably a good idea to replace it being a relatively cheap wear item. If you decide to replace it use AC Delco. Aftermarket CPAS's tend to have a high failure rate out of the box.
 

Mypetropig

Original poster
Member
Dec 29, 2011
226
Thanks I will try that. The idle is still stuck at 900 after being driven about 20 miles. While sitting at a stop light it surged to 1100 and came back to 900, did not stall and the air was on. If its not screwing up when I get the scan tool will I be wasting my time?
 

khill

Member
Jan 7, 2012
86
Trailblazers have a computerized system regulating air and fuel mixture. With increased rpms on an older vehicle, I would assume vacuum leak. Is it a gradual increase or moderate surge? Or is it a fast jump? Slow indicates vacuum leak from hose or seal. Fast indicates electrical or mechanical part suddenly not working right.


The MAF could play a role here, but mine doesn't have one, so I have no experience there.


If the O2 sensors aren't the problem, odd fuel mixtures can make them one later. Faulty O2 sensors can cause a range of issues from bad mileage to stalling when they send erroneous signals to the engine. Since it's not a continuous problem, just disconnecting them won't help you isolate the issue. You can get them cheapest on Amazon. These should be the ones.

Amazon.com: ACDelco 213-1574 OE Service Oxygen Sensor: Automotive

http://www.amazon.com/dp/B000C9HWQE/?tag=gmtnation-20


As to cruise control not working. I think I remember it doesn't work when the computer reads a problem that would affect the cruise control function. I remember mine wouldn't work when I had pending or lit codes for occasional misfires a while ago. Clearing those codes would fix it til they came around again. This is a pretty good indicator that you have codes stored in the car, even though the CEL isn't on.


Failing CPAS usually looks like incorrect timing, like a slipped or stretched timing chain. In serious cases, the vehicle would not shift and accelerate properly. It's pretty easy to see if a CPAS is fouled. First sign is oil in the connector, this can also foul up the wiring if oil starts to mess with the resistance when it seeps into the wiring insulation. You can also pop it out and look for signs of damage or plugging. Careful here, there is a bit of oil that will come out with the part, not too much, a few paper towels will sop it up. The CPAS has fine mesh screens in the notches that can get plugged by gunk in the oil affecting performance. Other times those screens can break loose into the CPAS or oil causing more problems. If you see any of these I would recommend replacing the part. Also, this part has been redesigned at least once since your TB was manufactured. While a good step, I doubt this is your problem, unless severely damaged, but then anything can happen with electronics. It is even possible for a CPAS to leak oil in the connector and still work perfectly.


If you replace anything with electricity going through it, always use AC Delco. It may be more expensive but these trucks can tell when they've been given the cheap stuff, and they don't like it :rotfl:



"If I do this it resets everything and it seems fine for a few days."

This comment tells me that you will find codes when the issue rears it's head. While I can't completely guarantee that code will be helpful, it usually is. It also is quick and typically free at most car parts places or independent mechanics.



Good luck,

Keith
 

CaptainXL

Member
Dec 4, 2011
2,445
Mypetropig said:
Thanks I will try that. The idle is still stuck at 900 after being driven about 20 miles. While sitting at a stop light it surged to 1100 and came back to 900, did not stall and the air was on. If its not screwing up when I get the scan tool will I be wasting my time?

Looking back a few replies on this thread I noticed Roadie said to check the Fuel Pressure regulator. I would check the fuel pressure and the vacuum hose as well. Also change the fuel filter if it has never been done. The fuel pressure regulator has a knack for leaking due to age.
 

Mypetropig

Original poster
Member
Dec 29, 2011
226
Just like yesterday the idle was stuck at 900 this morning but after driving just a couple of miles it came back to 600. Having a 6yr old and a 5month old makes it hard to find time to check things. I have the carb cleaner to check for vaccum leaks and had it checked for codes at autozone, no codes. I am still waiting to get my hands on a scan tool in hopes that it will reveal something.:banghead:
 

khill

Member
Jan 7, 2012
86
No dice on the generic codes eh... Sucks, but you might try to find a reputable mechanic in the area with an advanced scanner that can pull more than powertrain codes. There are different codes for different computer systems in the car that can only be read with a tech II or the like... Then again, it may be just another red herring...
 

Mypetropig

Original poster
Member
Dec 29, 2011
226

Mypetropig

Original poster
Member
Dec 29, 2011
226
My wife was out running errands today and the Service Engine Soon light finally came on. She had the code checked at Auto Zone PO340, cam shaft position sensor/ cuircut malfunction.
If its the sensor and I replace it will I need a case relearn or is that just for the crank sensor?
 

CaptainXL

Member
Dec 4, 2011
2,445
Mypetropig said:
My wife was out running errands today and the Service Engine Soon light finally came on. She had the code checked at Auto Zone PO340, cam shaft position sensor/ cuircut malfunction.
If its the sensor and I replace it will I need a case relearn or is that just for the crank sensor?

Just the crank I believe.
 

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