Idle problem

[Vettefan87]

Tonight after getting back from my vacation from California I took my car out for a drive and I noticed that the only time it has a problem idling is coming up to a stop. When coming up to a stop and I depress the break I notice the headlights dim and get brighter about 2-3 times every stop. Then when I come to a stop it idles kind of rough like it is going to stall but doesn't, then when I take off it kind of hesitates then runs fine. I didnt think to check the voltage but it did not flash over as being low. Could this be an alternator problem, but would that be causing the hesitations? Also I am getting no check engine light. Thanks



Justin

 

[Mika]

I have same problem and also when I stop idle doesn`t work properly. While driving no problems with engine. But if change gear to neutral or P then idle works fine. otherwise its too low around 500rpm and sometimes almost stalls while slowing down.

 

[SSTibet]

Rough Idle

Have a similar problem here folks... But I am guessing my problem is due to quality of fuel. At normal running speeds on the road no problem, but when I hit the traffic lights and stop the vehicle taking off becomes a problem due to rough idle. Hood starts shaking and I also get fuel odors inside the car... So the sypnosis is front hood shaking, fuel smelling, and I am grunting...

No idle problems though when the engine is cold... This problem does not happen all the time but sort of every other time or so when I take the car for a ride. I am a weekend driver with my Vette.

Any comments.

 

[Vettefan87]

My car will not run that bad. What mine does is like i said i will come up to a stop the idle kind of drops and while i am sitting there it kind of pulsates from about 450 to 650 RPM's, it has not stalled since the friday night right after I got the car back. Is this just something with the new motor or is it serious? Thanks



Justin

 

[Mika]

I also recently changed battery, IAC and alternator. So even those cannot cause this problem. Could it be some sensor problem because it only occors after engine is running in normal level?
And now this problem comes every time after engine is warm. A month ago the idle didn`t bother me every time.

 

[Crosschkm]

car dies

" have same problem and also when I stop idle doesn`t work properly. While driving no problems with engine. But if change gear to neutral or P then idle works fine. otherwise its too low around 500rpm and sometimes almost stalls while slowing down."

My buddy has the same problem on his 88, does anyone have an idea? We never get codes it will just die sometimes when he is coming off of the highway. The idle will drop to 500 or below and then die.

Cross
__________________

 

[Lteez]

I had that same problem with my 1987 it would run fine then all of a sudden this would happen it would cut off at stop lights I sprayed my throttle body with a cleaner and got injecter cleaner from the dealer and the problem went away....... I hope this helps

 

[Vettefan87]

This seems common with the 86-89 Corvette's or so except SSTibet, but he thinks he has his problem solved. I just ran the gas tank down to two bars with two bottles of Chevron Techron fuel system cleaner. and it has gotten a little better, the car has not stalled since the two times it did it a month ago, and the idle has gotten a little better, but I am concerned. I just had the motor rebuilt so I would hope they cleaned out the Throttle Body but you never know :eyerole . I am going to check the Throttle Body later tonight or tomorrow, and if it is dirty what do i spray in it and do I do it while it is running or off? Or do i just take a rag and clean it the best I can?



Justin

 

[vetteboy86]

One would think that when a corvette of these years idle's rough and dies a code would be set. I guess not however. I had a stumble problem, but mine accompanied a code.


Craig

 

[limomanb]

Have the same problem with my '86. When the engine is warm, it idles too low...between 500-600. No codes thrown either. When it gets down to 500..you can feel a little "shake" in the motor. I have no acceleration issues and the car generally runs fine otherwise. I put 2 bottles of Techron in today along with my gas fill-up. I always use premium fuels from big name stations like Shell,Exxon and Chevron.
How many miles should I expect to wait for the Techron to work?
If this doesn't work, I'll try a tune-up. It's due anyway. I'll spray the throttle body as well.

 

[vetteboy86]

Question for all of the above. Do any of you have bad hesitation problems with the car? Just trying to narrow the problem down.

Craig

 

[Vettefan87]

Have the same problem with my '86. When the engine is warm, it idles too low...between 500-600. No codes thrown either. When it gets down to 500..you can feel a little "shake" in the motor. I have no acceleration issues and the car generally runs fine otherwise. I put 2 bottles of Techron in today along with my gas fill-up. I always use premium fuels from big name stations like Shell,Exxon and Chevron.
How many miles should I expect to wait for the Techron to work?
If this doesn't work, I'll try a tune-up. It's due anyway. I'll spray the throttle body as well.

I checked my throttle body yesterday and it was filthy i cleaned it out with a rag the best i could. What do you spray them out with? and do you do it while the car is running or not?

 

[Hyde]

The best way to clean the T.B. is to remove it from the car. This allows you to remove the Idle Air passage cover on the bottom of the T.B. and clean the Idle Air Motor port.


Also, by removing it you can access the from the rear of it as well. You can also check the plenum.

If it still idles poorly you could check ignition timing and, eventhough it should set a code, the EGR.

Good luck.

 

[Vettefan87]

The shop took the timing back to factory specs which was around 6 degrees advanced. What should I take it to? I have the thermo master chip and the accel coil and wires. Thanks


Justin

 

[Hyde]

I would first focus on the TB. If this has never been cleaned, I would start here.

It is not difficult to remove, just a little time consuming. This is from memory so bear with...
MAKE SURE YOU HAVE REPLACEMENT GASKETS and coolant. see #9
1. Drain about 2 quarts of coolant. This should be enough to empty TB.
2. Loosen the band clamp securing air duct to TB.
3. Disconnect MAF connector and remove MAF and air duct together.
4. Disconnect TPS and IAC motor connectors.
5. There are two coolant lines to the TB. Remove them and cap off lines.
6. Disconnect air line for PCV.
7. Disconnect throttle linkage. Don't lose clips.
8. There is a vacuum line underneath. Remove four bolts holding TB to plenum and pull vac. line off.
9. The cleaning process is the whole point so attention to detail is important.
Remove any old gasket material from TB. You should have new TB to Plenum gasket, coolant/air passage cover gasket and IAC motor gasket.
10. Remove sensors and bottom cover (Torx bolts). Clean passages and gasket material. Keep in mind this TB is aluminum so do not overtighten when you reassemble.
11. Clean TB and reassemble.
12. Replace TB onto plenum. Your TPS/IAC motor need calibration. Let me know if you do not know how.
13. Reverse removal procedure. Pack coolant. replace MAF, etc.

Let me know how it goes. ANy questions feel free. Good luck.

 

[unleadedbrew]

I would first focus on the TB. If this has never been cleaned, I would start here.

12. Replace TB onto plenum. Your TPS/IAC motor need calibration. Let me know if you do not know how.

Gonna to clean my TB also, and could sure use some help in the calibration area, if you don't mind. ;help Thanx


Gordon

 

[Vettefan87]

Me too, I might pull the throttle body off this weekend but I do not know how to calibrate those either, if you could tell me how i would appreciate it. Thanks

Justin

 

[plumcrazy]

tps & iac setting

picked this up off the web somewhere.

hope it helps ya

How to Adjust your Early C4 TPS and Idle Speed
by Lars Grimsrud
SVE Automotive Restoration
Musclecar, Collector & Exotic Auto Repair & Restoration
Broomfield, CO Rev. New 6-15-00
This tech paper will discuss the procedure for correct adjustment of the Minimum Idle Speed and for adjustment of the Throttle Position Switch (TPS) on the early C4 Corvette TPI systems. These steps apply specifically to the 1985 model year, and in general to other years. Later model years do not have adjustable TPS's.
General
Idle speed and off-idle throttle response on the early TPI systems is determined by correct adjustment of the minimum idle speed screw combined with a correct setting of the TPS. I've seen many of these cars that have had their idle speed "corrected" by well-intentioned mechanics and owners by simply screwing the minimum idle speed screw in a few turns. This really messes up the settings, and will not make your car perform properly. Doing a correct setup of the TPS is one of the easiest ways to make your car feel and respond better. To maximize the benefit of this procedure, I recommend that you first remove your Throttle Body (TB), disassemble it (it's incredible easy - there are a total of about 5 pieces in it…), clean the TB up really good with some spray carb cleaner, and put it back together. A nice clean TB will really put an edge on the performance improvement you will get by doing this procedure.
The Service Manual has instructions for doing these operations, but the directions are scattered through several sections of the Manual. Here is the complete, step-by-step process for doing this (not including TB rebuild). All specs and steps are taken directly from the Manual (all 3 different sections), and this process is absolutely correct.
Tools & Equipment
You will need the following tools and equipment:
1. A set of Torx wrenches. You can buy a complete set in a nice, genuine plastic pouch at Sears.
2. A good digital voltmeter that will read voltages less than 1 volt.
3. A paper clip.
4. A small screwdriver.
Procedure
There are two electrical components on the TB that you will be working with: The TPS and the Idle Air Control Valve (IAC). Make sure that the connectors for these two components are easily accessible and that you can easily disconnect the IAC.
You will also be playing with the diagnostic connector under the dash. Remove the cover (if it's still in place). Bend your paper clip into a "U" shape. You will be playing with the two top right hand terminals ("A" and "B") in the connector.
First step is to set the minimum idle speed. If nobody has messed with this on your car before, the set screw will be covered by a pressed-in plug. It's located on the driver's side of the TB. Remove this plug if it's there.
With the IAC connected and the ignition "OFF," stick the paper clip into the diagnostic connector from "A" to "B." This grounds the diagnostic lead.
Turn the ignition to the "ON" position without starting the engine. Wait 30 seconds.
Now, with the ignition still in the "ON" position, disconnect the IAC connector at the IAC.
Remove the paper clip from the diagnostic connector.
Start the engine and allow it to reach normal operating temperature. The idle speed will probably be really low, and you may have to coax the engine a bit with the gas pedal to keep it running for a while.
If your car is an automatic, set the parking brake and put the transmission in "DRIVE." If your car is a manual, leave it in neutral.
Adjust the idle speed screw to obtain 400 rpm in drive or 450 in neutral.
Shut off the engine and re-connect the IAC.
That's it for idle speed. Now on to the TPS.
There are 3 wires stacked vertically on the TPS. You will need to be able to measure the voltage between the two top wires. You can either buy a special harness connector that breaks these wires out (from Mid America), or gently pierce the insulation of the wires with the pointy prongs on your volt meter. You can also stick a paper clip into each of the two top locations of the connector and clamp onto the paper clips to measure the voltage. Whatever is easiest for you.
Turn the ignition to the "ON" position without starting the engine.
Loosen the TPS Torx adjustment screws.
Set your volt meter to a low scale DC volt setting that will accurately read less than 1 volt.
Measure the voltage between the two top TPS wires.
Adjust the TPS by rotating its position until you get a reading of .54 volts.
Tighten the Torx screws and recheck the voltage. Re-adjust if necessary to make sure voltage is right at .54.
Turn the ignition "OFF."
You are now in perfect adjustment on idle speed and TPS output. Start the engine. It may take a few seconds for the car to "catch on" to its new settings.

 

[plumcrazy]

forgot to mention i set my idle a little bit higher 500-550 rpm seemed to
do the trick for me.

 

[Hyde]

Plumcrazy has it covered. I would do the TPS first though since you don't need the engine to run. Having the TPS cal'd. before the IAC may make it easier to maintain idle for IAC adj. Also, measure the IAC motor and make sure the distance from the shoulder of the housing to the end of the pintle is no longer than 1 1/8" . If it is, try pressing on the end to retract it (going slightly side to side can help). If that doesn't work then try decompressing pintle spring and turning the pintle clockwise(?). When reassemlbing, be sure to put the IAC motor on before attaching TB to plenum. The IAC can be a challenge to tighten when TB is on the car unless you have the right tools. I would leave the TPS off until it is ready for cal.

Don't forget to pack coolant.

Good luck.