High Idle on startup, then settles down.

[GreenBravada]

Searched and saw another post similar to this but with no resolution.

I bought a 2003 Bravada 4.2 with 188k miles. Did a CarFax and found that oil had been changed religiously until last owner got it three years ago (no records available). Car is in beautiful condition. Here's the problem:

When I first start it up, the idle is very high in the neighborhood of 1500 rpm. If I just sit there an wait for a minute or so, the idle gradually drops down to normal. Does this sound familiar to anyone?

I've read some maintenance threads here and am about to change filters, clean the throttle body, and all the usual things I do with a new vehicle, but it's been very cold where I am the past week or so.

Someone mentioned in a thread to try disconnecting the battery for 30 minutes, presumably to go back to the base programming and let the system relearn. The only code I have seen is for a large evap leak. I cleaned the really dirty gas cap and cleared the error. It stayed off and even passed our state eCheck test. But it is back now. The issue with the idle speed never changed while that was going on.

Any advice would be appreciated.

 

[Mooseman]

Don't disconnect the battery unless you plan to clean the throttle body at the same time. Could be the reason for the weird idle too if it was ever disconnected and not cleaned.

 

[GreenBravada]

Cleaning the throttle body is at the top of my list! I'm not going to play with the computer until I know the filters are clean and the throttle body is clean. Does this system have any sort of Mass Airflow Sensor MAF in the intake?

I should also track down this evap leak as well before doing anything fancy. It could be that the previous owner disconnected the battery trying to clear that error.

 

[Mooseman]

No MAF that year, just a MAP.

The evap leak could just be the gas cap. A common issue.

 

[GreenBravada]

Thanks very much for your help and advice, Mooseman. I've got all day tomorrow to poke around in there, do some cleaning, replace some filters, inspect all the rubber hoses for leaks. I'll have a better idea of what's up after that. Ordered a Gates gas cap and got sent the wrong one. Will try a new one before getting too deep into the evap system.

 

[mrrsm]

You did not mention this...But was there also a "Roaring Sound" during the elevated RPM period, too...perhaps involving the Electro-Viscous Hayden Fan Clutch?

 

[GreenBravada]

You did not mention this...But was there also a "Roaring Sound" during the elevated RPM period, too...perhaps involving the Electro-Viscous Hayden Fan Clutch?

I've read about issues with the viscous fan clutch, but I am going just by the engine sound from inside the car and the rpm on the tach. Can a failing fan actually affect the load on the engine and idle rpm?

I'll mention that I watched a YouTube video about an unrelated fix, and when the guy started his engine at the very end, it behaved just like mine with an initial high rpm (1300-1500) and the gradually coming down. All that tells me is that I'm not the first one to have his engine do this trick.

 

[TJBaker57]

When I first start it up, the idle is very high in the neighborhood of 1500 rpm. If I just sit there an wait for a minute or so, the idle gradually drops down to normal.

What rpm does it drop down to? Should be about 600.

 

[GreenBravada]

What rpm does it drop down to? Should be about 600.

I'm going out to work on it now, and can be more specific a bit later, but I'd say it is probably around 600. I know it's well below the 1000 line on the tach and idling smoothly. I'll check and get back to you. I think I have enough things to look into for now, so I'd maybe put this discussion to bed until I do some obvious things. All advice is greatly appreciated, but I need to do some basic things around the air intake system like cleaning the throttle body and checking for any possible air leaks.

 

[TJBaker57]

but I'd say it is probably around 600.

OK, that's good..I have a read about a condition where the PCM holds the idle up at about 900 though for the life of me I cannot remember what the issue was!

 

[mrrsm]

Yes... and mentioned in this Thread...by the Famous Alumnus "The Roadie":

intermittant high idle still

ok still have intermittant high idle problem. starts when I fill up with fuel and then immediatly drive on highway come to stop at next town 13km's idle up at about 950 stays up at 950 idle for 80 to 120km's then goes back to 650 and stays that way for rest of tankfull but if i fill up and go...

gmtnation.com

 

[GreenBravada]

Yes... and mentioned in this Thread...by the Famous Alumnus "The Roadie":

intermittant high idle still

ok still have intermittant high idle problem. starts when I fill up with fuel and then immediatly drive on highway come to stop at next town 13km's idle up at about 950 stays up at 950 idle for 80 to 120km's then goes back to 650 and stays that way for rest of tankfull but if i fill up and go...

gmtnation.com

These are different symptoms than I am experiencing. When the engine is cold, rpms start at about 1300 and stick there. If I wait 30-60 seconds, the rpms slowly come down to maybe 800 rpm. As the engine continues to warm up to normal operating temperature, the rpms drop down to about 600 which is normal. If I shut the engine down and restart, the rpm immediately goes to the normal 600 rpm. If I go into a store and come out (engine just sort of soaking in its heat) it starts and idles at 600 rpm. So, it seems to be entirely dependent upon the idle control reacting to what it sees as a cold engine.

Once the engine is even slightly warmed up, the engine operates in a completely normal fashion. So, I'm not going to jump to any conclusions until I have a chance to clean the throttle body and the PCV system and search for any vacuum leaks. Right now, my time is taken up with another vehicle, so I can't get into this yet. I DO very much APPRECIATE all the advice and suggestions, but don't want anyone to go to a lot of trouble on this until I can get the basic checks finished.

 

[mrrsm]

To completely eliminate the Mechanical aspects of the Electro-Mechanical Throttle Body... With the Air Plenum removed... an unorthodox way of seeing if the Butter-Fly Plate is in the least bit *Sticky*, apply Directed Hot Air around the TB metal surfaces, avoiding the "Gear Box" Housing and the Electrical Connections before starting up the engine and then see if it goes directly to the 600 +- RPM Level upon immediate Start-Up.

Note that the Throttle Body only regulates Air ...and No Fuel ever passes through any portion of it. Just avoid the areas of the Fuel Rail and EFIs while the Hot Air is being directed at around 300 Degrees F, impinging just upon on the Aluminum Body Surfaces for only around 20-30 Seconds.

 

[GreenBravada]

To completely eliminate the Mechanical aspects of the Electro-Mechanical Throttle Body... With the Air Plenum removed... an unorthodox way of seeing if the Butter-Fly Plate is in the least bit *Sticky*, apply Directed Hot Air around the TB metal surfaces, avoiding the "Gear Box" Housing and the Electrical Connections before starting up the engine and then see if it goes directly to the 600 +- RPM Level upon immediate Start-Up.

Note that the Throttle Body only regulates Air ...and No Fuel ever passes through any portion of it. Just avoid the areas of the Fuel Rail and EFIs while the Hot Air is being directed during this Targeted Location Aluminum Surfaces at around 300 Degrees, impinging just upon on the Aluminum Body for only around 20-30 Seconds.

Good info. I've got the tools to do that, but I think I might get to that after I try some other things! I'm pretty sure there are a few things that are semi-clogged or just plain dirty in this engine, so I'll do those basics first. The computer may just need a little bit of help to sort things out. If it still persists, we'll get down to the nitty gritty like Sherlock Holmes. What's that saying? "When you have eliminated the impossible, whatever remains, however improbable, must be the truth?"

 

[mrrsm]

...and... to his Good Friend, Dr. John Watson, "If convenient, come at once. If inconvenient... Come All The SAME!"

 

[Mooseman]

Some thoughts here. Has the evap leak been resolved? Has the throttle body been cleaned and the PCM reset by disconnecting the battery? You indicated they were at the top of your list but never confirmed.

Another thing to check is that the intake manifold bolts are tight. If there is a little bit of air getting in while in open loop, it doesn't know to adjust the amount of fuel until the O2 sensor starts working in closed loop or the leak closes up as it warms up. The leak could be so minimal that in closed loop it's not enough to trigger a lean condition code.

Should be 89 in-lb.

Should also check for vacuum leaks for the same reasons.

Edit: Just saw in your other thread that you're still working on the evap leak.