ColoradoRaptor
Headbanging Hillbilly
- Location
- Canon City, Crawlorado
Check your temp sensors!
Ok, still having a high idle issue.......
- Thread starter YELLAHEEP
- Start date
YELLAHEEP
NAXJA Forum User
- Location
- Littleton, Colorado
Reaching maximum level of frustration here.........
Things done:
-Replaced both the TPS and IAC with brand new units
-Sprayed carb cleaner all around the intake and found no leaks.
-Checked all vacuum lines to the Emissions evap system and vac. accessories including the vacuum ball. No leaks.
-Checked the brake vac. booster - holds vac. just fine.
-Plugged all external vacuum sources at the manifold - no change in idle or performance - all vacuum systems appear in good working order.
-Disconnected the battery for 30 min. to reset the ECU.
The original problems started when the TPS went bad all of a sudden on a cold start up. Caused shifting/rpm issues - totally undriveable. Codes were set. Replaced the TPS and all was fine for a few days, then the high idle started.
Haven't had any codes set since - nor has it really done any stuttering. Occasionally, after being driven and warmed up, it won't fire while cranking unless I press the gas pedal to the floor - then it roars to life.
What is constant seems to be the 1,000 rpm idle. Every once in a while it'll fall to around 900/850 when it's good and warm, but mostly, stays at 1,000.
The driving concern is that the rpm takes 3-4 seconds to come down from driving rpms (ie: 2200 at highway, or 1800 - 2000 rpm in town) when I go to stop at a light or stop sign. It actually pushes forward while lightly applying the brake which is a bit scary.
Where does the IAC get it's signal from? It just seems like the IAC is closing the port too slowly.
Any other suggestions? This sucks. My next attempt may be swapping in a different ECU......... :dunno:
Things done:
-Replaced both the TPS and IAC with brand new units
-Sprayed carb cleaner all around the intake and found no leaks.
-Checked all vacuum lines to the Emissions evap system and vac. accessories including the vacuum ball. No leaks.
-Checked the brake vac. booster - holds vac. just fine.
-Plugged all external vacuum sources at the manifold - no change in idle or performance - all vacuum systems appear in good working order.
-Disconnected the battery for 30 min. to reset the ECU.
The original problems started when the TPS went bad all of a sudden on a cold start up. Caused shifting/rpm issues - totally undriveable. Codes were set. Replaced the TPS and all was fine for a few days, then the high idle started.
Haven't had any codes set since - nor has it really done any stuttering. Occasionally, after being driven and warmed up, it won't fire while cranking unless I press the gas pedal to the floor - then it roars to life.
What is constant seems to be the 1,000 rpm idle. Every once in a while it'll fall to around 900/850 when it's good and warm, but mostly, stays at 1,000.
The driving concern is that the rpm takes 3-4 seconds to come down from driving rpms (ie: 2200 at highway, or 1800 - 2000 rpm in town) when I go to stop at a light or stop sign. It actually pushes forward while lightly applying the brake which is a bit scary.
Where does the IAC get it's signal from? It just seems like the IAC is closing the port too slowly.
Any other suggestions? This sucks. My next attempt may be swapping in a different ECU......... :dunno:
- Location
- on the beach in Ocean View, VA
TPS and CPS tell the ECU what your throttle is doing (closing) and what your engine speed is (should be idling). The ECU uses this info to send electricity to the IAC to close to correct location for expected idle speed. IF everything else is functioning correctly (i.e. no vacuum leaks, correct CPS signal, correct throttle position signal, and no leaking injectors) I would look into the signal from the ECU to the IAC. I don't know where to get the specific values that you should be looking for, but I'm sure someone will chime in with them.
I have to admit, however, I don't recall ever seeing a "returns to idle slowly" being caused by faulty ECU signal. It's always been either "no signal" or "good signal with external factor" causing poor idle condition.
best of luck with it:looney:
I have to admit, however, I don't recall ever seeing a "returns to idle slowly" being caused by faulty ECU signal. It's always been either "no signal" or "good signal with external factor" causing poor idle condition.
best of luck with it:looney:
RichP
NAXJA Forum User
- Location
- Effort, Pa
Every high idle I have ever seen is from a leak, the past two were from a loose and a missing last bolt in the intake/exhaust manifolds. Just to be sure retorque your manifold bolts to 27 ft lbs.
Frank Z
NAXJA Forum User
- Location
- Colorado Springs
Troy,
Have you inspected the butterfly to see if it's installed correctly? Yeah ir sounds kinda stupid, but there is a beveled edge on two different sides of the butterfly. Can't hurt to pop the air tube off and have a close look. Hell I'd try swapping the throttle body off a properly running rig at this point.
I know you've used carb and choke cleaner to check for vacuum leaks, but I'd suggest using propane instead. It will cause a very audible increase in RPM's.
Have you inspected the butterfly to see if it's installed correctly? Yeah ir sounds kinda stupid, but there is a beveled edge on two different sides of the butterfly. Can't hurt to pop the air tube off and have a close look. Hell I'd try swapping the throttle body off a properly running rig at this point.
I know you've used carb and choke cleaner to check for vacuum leaks, but I'd suggest using propane instead. It will cause a very audible increase in RPM's.
YELLAHEEP
NAXJA Forum User
- Location
- Littleton, Colorado
I doubt the butterfly would be bad. This problem started happening after the TPS went bad. Prior to that, the rig ran great - I did swap out the entire throttle body with another one just for grins but it didn't change anything and I've since replaced it with the original throttle body.
Unfortunately all other properly running rigs I have around here are either Renix or a '99. I looked at the '99 and the IAC harness plug is different.
I've got a couple of small bottle torches here - I'll try using one of those to once again check for a vac. leak.
I'll also look closer at the MAP sensor as you've suggested in the other link.
grrrrrrrr........ :banghead:
RichP
NAXJA Forum User
- Location
- Effort, Pa
The reason I suggested re-torquing the manifolds is you mentioned it runs different between cold and hot. The stock bolts, nuts and tension washer can change as the tension washer ages and looses it's springiness. One of the ones I worked on ran fine cold then got progressively worse as the engine got hot, loose rear bolt, torqued it and that took care of it.
Frank Z
NAXJA Forum User
- Location
- Colorado Springs
Agreed that the butterfly would be highly unlikely, but since you've really been chasing a phantom I thought it would be worh a quick look anyway.
- Location
- MilkyWay Galaxy
My money would be on ground wire gremlins. The brakes dump a bunch of voltage to ground for the brake lights, and a poor ground connection(s) can back feed into the TPS / ECU grounds and cause idle annomollies big time with Renix. They seemed to have solved the problem in the 91.
YELLAHEEP
NAXJA Forum User
- Location
- Littleton, Colorado
Yeah, I'm not thinking this is the issue - it doesn't have problems when I press the brake pedal....... and this rig is a '96, so no Renix.
- Location
- MilkyWay Galaxy
OK, so its NOT the Renix.
The brake switch also signals the ECU & TCU as well as turning on the brake lights. If that signal to the ECU & TCU is compromised the ECU may be late to drop the rpms while braking. I am not sure of the later years exact wiring layout, but their is a connection between them.
RichP's suggestion is still valid. IIRC you can also check for a vacuum leak by closing off the air supply to the IAC inlet port. With it covered the engine should die (or nearly die as it still gets some air via the CCV valve cover line), unless there is a vac leak gremlin still mucking about.
Don't forget a loose valve cover gasket can be a vac leak to the CCV line that bypasses the throttle body!
The brake switch also signals the ECU & TCU as well as turning on the brake lights. If that signal to the ECU & TCU is compromised the ECU may be late to drop the rpms while braking. I am not sure of the later years exact wiring layout, but their is a connection between them.
RichP's suggestion is still valid. IIRC you can also check for a vacuum leak by closing off the air supply to the IAC inlet port. With it covered the engine should die (or nearly die as it still gets some air via the CCV valve cover line), unless there is a vac leak gremlin still mucking about.
Don't forget a loose valve cover gasket can be a vac leak to the CCV line that bypasses the throttle body!
- Location
- Torrance, CA
What is a used PCM going to do for you? 110% your PCM isn't bad. If anything you should be looking for a used tach.lawsoncl
NAXJA Forum User
- Location
- North Idaho
How do you know the tach is correct? I'd be very surprised if the readings from the PCM port are wrong and the engine is running correctly (aside from a high idle). What's it idling at?
- Location
- NJ, U.S.A.
Did they say how they verified the correctness of the tachometer?
