1988 2500 Fast idle
kesen84401
10-07-2003, 01:48 PM
Have a 1988 k2500 with 350 w/ throttle body. Will not come out of fast idle. Check engine light works and is not on. I have replaced throttle position sensor, coolant temperature sensor, oxygen sensor, and checked throttle body for leaks. Any help/suggestions woulb be appreciated.
Ken in Colorado
Ken in Colorado
Sexy beast
10-07-2003, 02:13 PM
are you sure there aren't any leaks? check all your hoses.
BOOZER
10-10-2003, 11:04 AM
It's common to see these suck a t/b base gasket &
you might not be able to tell w/o removing it. Also you replaced everything except the I.A.C. valve???
The idle air control motor alows the ecm to adjust &
control idle rpm, remove & inspect for debris. And I second S/B on an old vehicle, check all vac hoses.
To diag the iac youll need a serv manual to check the valve, harness-connectors & ecm.
you might not be able to tell w/o removing it. Also you replaced everything except the I.A.C. valve???
The idle air control motor alows the ecm to adjust &
control idle rpm, remove & inspect for debris. And I second S/B on an old vehicle, check all vac hoses.
To diag the iac youll need a serv manual to check the valve, harness-connectors & ecm.
kesen84401
10-17-2003, 04:16 PM
It's common to see these suck a t/b base gasket &
you might not be able to tell w/o removing it. Also you replaced everything except the I.A.C. valve???
The idle air control motor alows the ecm to adjust &
control idle rpm, remove & inspect for debris. And I second S/B on an old vehicle, check all vac hoses.
To diag the iac youll need a serv manual to check the valve, harness-connectors & ecm.
I can find no leaks (yet) and have checked the t/b gasket by removing t/b. Also checked by spraying carb cleaner all around t/b and noted no change in idle. Might also note that idling, my truck does not sound un-normal. It does sound "high" when operating (i.e. sounds "rapped out" at 55mph) this does change (or at least has) to normal operation after on to three hours of operating (I noticed when driving from Colorado to Idaho, like it shifts to overdrive and runs quietly).
you might not be able to tell w/o removing it. Also you replaced everything except the I.A.C. valve???
The idle air control motor alows the ecm to adjust &
control idle rpm, remove & inspect for debris. And I second S/B on an old vehicle, check all vac hoses.
To diag the iac youll need a serv manual to check the valve, harness-connectors & ecm.
I can find no leaks (yet) and have checked the t/b gasket by removing t/b. Also checked by spraying carb cleaner all around t/b and noted no change in idle. Might also note that idling, my truck does not sound un-normal. It does sound "high" when operating (i.e. sounds "rapped out" at 55mph) this does change (or at least has) to normal operation after on to three hours of operating (I noticed when driving from Colorado to Idaho, like it shifts to overdrive and runs quietly).
BOOZER
10-17-2003, 05:05 PM
You still did not mention a thing about checking the I.A.C. valve. Now you say it dosnt sound "un-normal". ??????????????????????????????????
So it's idle RPM is what?
If your getting a roaring sound, look for a defective
fan clutch thats not disengauging.The clutches are both RPM & thermally sensitive to disengague when not needed.
So it's idle RPM is what?
If your getting a roaring sound, look for a defective
fan clutch thats not disengauging.The clutches are both RPM & thermally sensitive to disengague when not needed.
kesen84401
10-18-2003, 03:45 PM
I pulled IAC from T/B, can't tell if good or not (I didn't know it was there until your post, thank you.) I will replace on Monday when one is available. On the fan clutch note: That is what the engine sounds like, meaning bad fan clutch. It was also the first thing I checked, sorry for not mentioning that.
Automotive Network, Inc., Copyright ©2025