1995 Yukon High Idle

[Steven94]

My 1995 Yukon is having a high idle issue and I've already replaced the EGR valve, EGR Solenoid, TPS and its still having issues any help is appreciated.

 

[B-train]

Check the gasket under the TBI unit. They are known to crack and disintegrate with age. This will cause a huge air leak and allow it to run faster. Thise didn't use MAF sensors, so the engine doesn't know it's getting more air than it realizes.

 

[Eman85]

95, is it a Vortec engine? If TBI then it's most likely the throttle body gasket. If you have a scan tool check IAC and see if it's being commanded closed, if so it's a vacum leak. A smoke generator is a good way to test for a vacum leak, easy to make one from PVC pipe and Youtube videos.

 

[exp500]

Read the manual section for resetting Idle Air Control. Thats 1st step.

 

[Steven94]

Would a vacuum leak also cause it to have a low idle? Like low to were it sounds like it’s about to die?

 

[exp500]

Your computer also shows codes - OBD1 flashing light on dash then count flashes with proper pins jumpered.
Even disconnecting the battery or dead battery could cause IAC calibration issues.
Download here and search for IAC and OBD to start your servicing education.
- https://www.gmt400.com/threads/88-95-service-manuals.43575/

 

[Eman85]

Let's all get on the same page here.
Is this a 95 with a Vortec 350??
You said you had a high idle now you're talking about low idle.

 

[Fless]

Let's all get on the same page here.
Is this a 95 with a Vortec 350??
You said you had a high idle now you're talking about low idle.

Details, details, details.

 

[Steven94]

Let's all get on the same page here.
Is this a 95 with a Vortec 350??
You said you had a high idle now you're talking about low idle.

Sorry, 1995 Yukon 5.7 it has a low idle when turning on like 500 rpm almost to the point of dying. Once your driving the rpms will shoot up to about 1500rpm if you put it in park. While driving at idle at a light or stop sign its around 800-1000rpm. I have changed the Egr valve, Egr solenoid, TPS, and the Idle air control valve to this point.

 

[Eman85]

Is it a Vortec motor? Have you checked for any codes? Did you clean the throttle body and mass airflow sensor and check the air filter and all of the intake duct hoses? Have you checked for any vacum leaks? Do you have a scan tool with the ability to read live data? How much money is in your checkbook to keep buying parts? We can fire the diagnostic parts cannon if you want.

 

[strutaeng]

Vortec started in 1996.

All OP apparently knows is that his engine is a 5.7 350...

 

[east302]

Once your driving the rpms will shoot up to about 1500rpm if you put it in park. While driving at idle at a light or stop sign its around 800-1000rpm.

Is it happening only when the brakes are applied (brake booster)?

GM published diagnostic procedures in the manual. The link is in post #6, but here is an example from the 95 manual:

 

[GMCChevy]

At this point rather then continuing to throw psrts at it you should probably use a scan tool thst shows what the different sensors are reading so you can either pinpoint which one is bad or what reading isn't at a normal level.

 

[Steven94]

Is it happening only when the brakes are applied (brake booster)?

GM published diagnostic procedures in the manual. The link is in post #6, but here is an example from the 95 manual:

View attachment 446265
View attachment 446266

High idle starts after driving low idle starts as soon as I turn it on but sometimes it’ll start to high idle after a few minutes warming up

 

[Steven94]

At this point rather then continuing to throw psrts at it you should probably use a scan tool thst shows what the different sensors are reading so you can either pinpoint which one is bad or what reading isn't at a normal level.

Waiting for it to come in