My '02 Tahoe L59 revs WAY too high on cold start ups. Anyone got any ideas?

[Marky Dissod]

Whenever I start my '02 Tahoe L59 cold (6 hrs cooldown or more), the engine briefly revs up over 1600RpM.
This morning, it wasn't even freezing outside, yet it revved itself to 2000RpM for a few seconds before settling down to 1000RpM.
The first five minutes, I REALLY gotta lean on the brake, or I'll flatten some oblivious idiotard in the crosswalk.
Physical throttle cable, by the way.

Although I doubt I would mind this problem if it were already April, another 3 months of winter cold starts scares me stupid.

How do I get the cold starts to not rev so damn high? Disconnect battery power for a few hours?

 

[Scottydoggs]

try cleaning the tb. air intake off open the butterfly and clean as much of the black crap out on the walls and the back side of the butterfly.

carb and choke cleaner and a old tooth brush and some rags does a good job to clean with.

 

[strutaeng]

Hook up a scanner with live data and try to see if the sensor reported values seem correct, or ballpark.

Does your truck have EGR? You may a vacuum leak that seals itself up after the engine warms up due to a gasket expanding and sealing from thermal expansion.

Probably wise to do a smoke test, but live data scanner will most likely give you enough information to determine what's the issue.

 

[iamdub]

I agree with the above replies and would add removing the IAC valve and cleaning the pintle and the seat in the side of the TB where it seals to. But, first, check the commanded versus actual throttle angle (should be expressed as %).

 

[Marky Dissod]

Appreciate your replies. Found a near-as-makes-no-difference identical throttle body assembly off an '02 GMT800.
Given that my IAC motor and Throttle Position Sensor are both at least 22 years old, should I fire the Genuine AC Delco parts derringer and get a new IAC motor & Throttle Position Sensor, and clean the ever-lovin schidt out of the throttle body?

Also, besides disconnecting the battery for a few hours, is there anything else I can do?
Is there such a thing as a 'throttle relearn' procedure, or anything else of that nature?

 

[iamdub]

Appreciate your replies. Found a near-as-makes-no-difference identical throttle body assembly off an '02 GMT800.
Given that my IAC motor and Throttle Position Sensor are both at least 22 years old, should I fire the Genuine AC Delco parts derringer and get a new IAC motor & Throttle Position Sensor, and clean the ever-lovin schidt out of the throttle body?

I'm always for proper diagnostics. But, if you're good with doing so, I wouldn't see it as being a total waste. Surely, being 22 years old and a lot more electromechanical than the newer ones, it would have some wear.

Also, besides disconnecting the battery for a few hours, is there anything else I can do?
Is there such a thing as a 'throttle relearn' procedure, or anything else of that nature?

You can reset the PCM to where it has to relearn idle. The proper way is to initiate it with a bi-directional scanner. I can't recommend it, but I've never had a problem doing it the backyard way of pulling the PCM fuses while it's running. You do that, turn the key off, replace the fuses then start it. It'll likely stall immediately. Just restart it. Don't give it throttle to keep it running. Let it figure it out on its own. If it starts and runs as it did before, then it didn't reset.

 

[strutaeng]

Is this drive by (edit) cable, right? Is there such thing as throttle relearn on that?

I've never wondered. Somehow I think that's just for drive by wire? IDK

 

[iamdub]

Is this drive by wire, right? Is there such thing as throttle relearn on that?

I've never wondered. Somehow I think that's just for drive by wire? IDK

'02 has a cable, IAC and separate TPS. The PCM uses the IAC to control the throttle.

On DBW, the PCM just opens the throttle blade to control idle.

 

[strutaeng]

'02 has a cable, IAC and separate TPS. The PCM uses the IAC to control the throttle.

On DBW, the PCM just opens the throttle blade to control idle.

Oops, meant drive by cable on my first sentence...will edit.

 

[Marky Dissod]

Physical real throttle.

 

[Doubeleive]

Physical real throttle.

just clean it, like clean it good, take the iac out and clean it and clean inside where it bolts up, I suspect you will see a lot of black soot
that should resolve the problem. If not then grab one from a junkyard do the same and put it on.
trying to a find a new IAc unless you get lucky and score a new genuine oem one then forget it because none of the aftermarket ones work right, at least none I ever found.
it should self relearn within a couple minutes if all goes well

 

[Doubeleive]

Appreciate your replies. Found a near-as-makes-no-difference identical throttle body assembly off an '02 GMT800.
Given that my IAC motor and Throttle Position Sensor are both at least 22 years old, should I fire the Genuine AC Delco parts derringer and get a new IAC motor & Throttle Position Sensor, and clean the ever-lovin schidt out of the throttle body?

Also, besides disconnecting the battery for a few hours, is there anything else I can do?
Is there such a thing as a 'throttle relearn' procedure, or anything else of that nature?

shouldn't even have to mess with the battery, after 2-3 times of starting and letting it idle down on it's own it should self relearn

 

[Doubeleive]

I have always had good luck with throttle bodys and never had any relearn issue's out of all the countless times I have replaced or cleaned them which I sometimes clean every 3 months or so, but for whatever reason this made me think way back when I had a pos carbureted mazda and was doing whatever to the carb and inadvertenly pushed the vacuum advance up, boy that made it fun to drive! felt like driving a porsche compared to a scooter.

Vacuum Advance w/Aftermarket Carbs - RX7Club.com - Mazda RX7 Forum

1st Generation Specific (1979-1985) - Vacuum Advance w/Aftermarket Carbs - I have a Rotary Engineering twin 36DCD setup on a stock port 12A with a Racing Beat exhaust system. I received the kit used, in somewhat rough condition, so I made a lot of updates, including adding a vacuum port on one...

www.rx7club.com

 

[ivin74]

Physical real throttle.

Have you checked for any vacuum leaks?

 

[Marky Dissod]

Have you checked for any vacuum leaks?

A smoke check was done and passed, but the entire intake in front of the throttle body was removed before it.
Might need to check again between the MAF & the throttle body, since that's how the engine normally operates.
Also, the engine was totally warmed up, so maybe the smoke test should be performed COLD.

 

[Doubeleive]

A smoke check was done and passed, but the entire intake in front of the throttle body was removed before it.
Might need to check again between the MAF & the throttle body, since that's how the engine normally operates.
Also, the engine was totally warmed up, so maybe the smoke test should be performed COLD.

meh I don't know if a smoke test is going to help or even find anything.
I would be looking primarily at the throttle body, maf, temperature sensor readings (previous to cold start and on cold start)
if you had that bad of a vacuum leak you would be having other issue's as well
how many miles are on this vehicle?

 

[Marky Dissod]

160,061 this morning.
Found myself nervously starting in 'N' and almost immediately shifting into 'D' to keep the cold start RpM under 2500.

Yanked out two fuses that said 'pcm' in the underhood fusebox. Will plug them in just before the next time I start it, see if that helps.
If not, guess I gotta find a clever diagnostic mech?

 

[Doubeleive]

160,061 this morning.
Found myself nervously starting in 'N' and almost immediately shifting into 'D' to keep the cold start RpM under 2500.

Yanked out two fuses that said 'pcm' in the underhood fusebox. Will plug them in just before the next time I start it, see if that helps.
If not, guess I gotta find a clever diagnostic mech?

not necessarily
you could try unplugging the maf, this should put everything in a default setting. start it and see if it does anything different
also use a obd scanner and find the ambient temperture reading, see what it says (pre-start key on only) versus actual temperature & also the temperature sensor on the block, there should be a reading for that somewhere.
the reason for checking temperature reading is if it is showing it is like -40 or even 80+ when it's really not this could maybe be a cause or part of the problem
@rockola1971 may be able to provide more detailed information on the related issues that could make the idle high on a cold start aside from a funky throttle body or iac

 

[Marky Dissod]

You may very well be right. Although I've never understood why, 'arctic' cold starts correlate with higher RpM starts.
If the engine somehow thinks it's even colder than it actually is, that could be one possible explanation.

I'll find a mech to provide me with the temp sensors' readings later this week.
Hoping for @rockola1971 's counsel.

 

[Doubeleive]

have you looked at the throttle body when it is cold, like taken the intake housing off and gave the buttrerfly a couple flips to see if it is sticky or anything?