Hey so I've been trying to solve this problem for a bit now, and I'm try to go back to the basics and I hope someone here can give some insight. 1989 GMC C1500 5.0L Auto 2WD
Symptoms:
-Hesitation right when you press the throttle(mostly noticeable from a stop)
-Abnormal idle surge/stalling for about 5 seconds
-High Idle(anywhere from 800-1300 rpms)
-Loss of power underload(sort of like if the ignition advance curve stops)
As to when these things happen it is very intermittent and very hard to reproduce on command. I notice it most after about 20-30min of driving, however it sometimes doesn't happen at all.
Things I do know:
-There are no vacuum leaks(with the IAC fully closed idle is perfect)
-Timing chain slack is in specification
-The IAC is functioning, however as far as the high idle goes it seems as if the ECU is telling it to raise the idle for a reason I'm not quite sure of.
-I have tried 2 different TPS and MAP sensors that I had laying around with no noticeable change in the symptoms.
-My fuel pressure is in specification.
-Distributor Shaft does not have any noticeable radial play.
-Coolant sensor seems to have the appropriate resistance values.
-The injectors have a clean spray pattern.
-I have tried a second ECU I have, however it literally just wanted to high idle all of the time, even as high as 1600rpms.
Items that I think may be of concern at this time:
-The IAC(not sure how they work internally but maybe its missing a few teeth on a gear or something?)
-The distributor cap and rotor are not in the best shape.
-The ignition coil(its about 1-2 years old but seems like it could cause some of these symptoms.
-The Ignition control module(It is new from napa but the lack of power I feel relates to this part the most)
-The TPS(maybe the voltage setting isn't perfect, but I don't see it causing this much of a problem, especially intermittently)
-Lack of grounds from the engine to the chassis(just a theory)
So if anyone can give any input from their own experiences or even just refresh my memory on how each part works I would appreciate any information regarding this issue.
Thank you
Symptoms:
-Hesitation right when you press the throttle(mostly noticeable from a stop)
-Abnormal idle surge/stalling for about 5 seconds
-High Idle(anywhere from 800-1300 rpms)
-Loss of power underload(sort of like if the ignition advance curve stops)
As to when these things happen it is very intermittent and very hard to reproduce on command. I notice it most after about 20-30min of driving, however it sometimes doesn't happen at all.
Things I do know:
-There are no vacuum leaks(with the IAC fully closed idle is perfect)
-Timing chain slack is in specification
-The IAC is functioning, however as far as the high idle goes it seems as if the ECU is telling it to raise the idle for a reason I'm not quite sure of.
-I have tried 2 different TPS and MAP sensors that I had laying around with no noticeable change in the symptoms.
-My fuel pressure is in specification.
-Distributor Shaft does not have any noticeable radial play.
-Coolant sensor seems to have the appropriate resistance values.
-The injectors have a clean spray pattern.
-I have tried a second ECU I have, however it literally just wanted to high idle all of the time, even as high as 1600rpms.
Items that I think may be of concern at this time:
-The IAC(not sure how they work internally but maybe its missing a few teeth on a gear or something?)
-The distributor cap and rotor are not in the best shape.
-The ignition coil(its about 1-2 years old but seems like it could cause some of these symptoms.
-The Ignition control module(It is new from napa but the lack of power I feel relates to this part the most)
-The TPS(maybe the voltage setting isn't perfect, but I don't see it causing this much of a problem, especially intermittently)
-Lack of grounds from the engine to the chassis(just a theory)
So if anyone can give any input from their own experiences or even just refresh my memory on how each part works I would appreciate any information regarding this issue.
Thank you