High idle
 

I just went out this morning to reset my ignition timing - found out that it was set to 5? instead of the normal 10? - and after resetting it, it was idling at ~1600 -- way too high. It was a solid 1600, but even after warming up, it still rested ~1000, 300 off from the standard 700. ISC? MAF? IAT Sensor? Or something I'm totally missing... I cleaned my ISC about 2 months ago, tested my MAF 1 month ago as well as my IAT sensor. O2 sensor is ~3 months old.

I couldn't find anything in the TSRM that dealt with a high idle; only rough / erratic, but mine is smooth. Ideas?

There should be an air screw on the front side of the intake manifold just right over the butterfly. Try screwing it in some and see if that helps. You might have knocked off a vacuum hose, but that amount of timing sounds like just a turn or so on that air screw should do it for you.


Russ

did you do the ign timing with the diagnostic pins connected?

yea i would try vacuum leaks.... do you have an aftermarket boost gauge?

get some carby cleaner and spray around the intake and vacuum areas and see if your idle changes

if it does... you've found your leak :)

Actually, I've got an NA :( No turbo here...

I'm fairly certain I have a leak somewhere along my intake as it's starting to crack around the lip of the angle tube - I'm still looking for a replacement aftermarket solution, but for NAs, there seems to be very little that has just the tube.

ahhh k i'll reword it... if you had an aftermarket vacuum gauge you could see what your vacuum is at idle and you'd know straight away if you had a leak :)

if you have any cracks in piping between the afm and throttle body or intake manifold leaks or vacuum leaks this will screw with your idle

A possiblity until you find another tube is to put some silicone on the cracks. That will seal them up, plus remember the vacuum hose under the tbe that connects to the power steering pump. It is just a bit easier not being turbo charged in finding a leak, but there are a lot of vacuum hoses to check, so the spray is the easiest way to check it out. Even an open EGR valve will mess with the idle.


Russ:dunno:

I'm going to go w/ a compression test - too much work to play guessing games on my daily driver :(

I'm assuming a BHG will also distort idle... grabbed a test kit today, just waiting for the car to cool off so I can test it.

A blown head gasket will distort the idle in that it will cause a missfire as water or oil gets on the plug and fouls it out. An air leak of somesort is what will cause the higher idle speed. If you have an air leak in the tube anywhere before the butterfly valve then the idle will be lower because of not allowing the airflow meter vane to open like it should. Anywhere on or after the butterfly valve will cause the higher idle. I could be the cable that is not allowing the throttle to close all the way, or a gasket blown out somewhere along the intake.


It could even be your distributor. It may have come loose and is advanced too far. There are enough vacuum hoses to cause the higher idle and like the girl said, spray WD 40 around the intake and hoses, lightly, and see if the idle changes any. You could also get a stethescope and listen carefully and see if you can hear a place where air might be getting in unwanted. If you find a BHG, then never mind, as that has to be fixed first.

Even the idle speed control valve could go bad.

Russ

Head gasket tested good :D

Now to investigate why else... I also flushed the heck out of my system, found a lot of rust deposits in there.

Going to re-wire the condenser fan so it's on all the time.

Anyone have any reccommendations for an electric fan to replace the clutch one? Also installation tips?

In regards to what I read in another thread, how effective is turning the heater on in regards to dumping heat? I bypassed my heater control valve so it helps it run slightly cooler, but not by much. Haven't tested the heating problems since testing the block / head and flushing / adding proper mix of coolant since it's 100+ outside and I just don't have the energy with my car having no A/C. As of today before the flush / test, idle was still high. Going to check my ISC again tomorrow.

A few guys have bought radiators from Fluidyne and have very good results. I bought an aftermarked race aluminum for mine and in the 100+ here, it never moves, even with the heater turned to 65. I bought the large 16" fan from Advanced Auto, all of the parts houses carry these things. I also have an adjustable temp sensor for the fan so I can dial in the temp I want it to go off and with this radiator it doesn't stay on long. Just take off the fan clutch and put four small bolts to hold the pulley and go with the electric fan.


The stupid thing about the heater core being used to help the engine cool is that it works!! That means running the heater in the summer to help it cool down. To me, that shows that the stock radiator is very inadequate. It is nice but very thin. Fine for up north I guess but not for down here in the south. Make sure the system is flushed and flowing very well, maybe even let the flush run through it a bit longer than the instructions state and do it several times.

Try water wetter too, it does help a little. I really think you have to have a piece of metal under the airdam to the frame under the radiator to keep the air flowing into the rad and not back out under the car first. Make sure the condensor is clear too. I didn't make a shroud for my electric fan and bigger radiator and it doesn't need one, but the stock radiator definately needs the shroud.

Well good luck with it.

Russ

Thanks for your help thus-far; still need to check out the ISC but not really enough time with Rita about to slam into the coast here; hopefully I'll have some time to check it in the near future.

I forget, but isn't the ISC a testable part electrically? I know that carbon buildup on the sensor will cause problems, but I'm not sure if the valve itself has gone bad yet.

The part can be tested. Suprrrrrrra-girl, whoops too many r's, had a link to a service manual that would probably tell you exactly what to test and the values. I have a cd service manual, but I can't figure out how to copy it to here. Ask her for that link.

Russ

I'd adjusted the screw - you're talking about the one near the throttle body, right? I adjusted it to the lowest RPM position and it's still idling too high (I knew it was the lowest RPM position because the other direction revved the engine higher)

The cams still stock? On a larger motor a massive cam will bump the idle up. My 350 has to idle at about 11-1200 after warming up to keep the lope from the cam from killing it.

Yep, still stock - only thing that isn't stock in regards to engine parts is the air filter.

If you have that idle adjuster screw all the way in then you have either an air leak or the ISC is not functioning. You can hear the ISC clicking when you turn the A/C on and off, it should do a little clicking, but that still won't guarantee that it is working. If the computer senses that the car is always cold then it will keep the idle up too, there is a sensor for that too. Still sounds like a vacuum leak though. Make sure that the screw you were playing with seats in all the way too. Sometimes all the carbon build up won't allow it to seat when screwed in all the way. Also, if all else has been checked, the brake booster could be leaking air. Just pinch off the hose to it to check that one out.


Keep trying!

Russ

The old carb cleaner test.
 

You can always do the old carb cleaner test, and give spritz here and there to see if the idle changes. Spritz around the intake, and vacuum lines, and what not, if you get a change in your idle when spritz it in a certain area, then that is where your vacuum leak would be.

=( No suction of the carby spray along the intake / TB assembly... not sure where else my leak would be at if I'm suffering one. I did notice though that the idle has reset itself slightly, now idling at the mid 800s - still higher than stock. Would having the K&N cone filter distort the idle w/o a different MAF sensor?

800 is very close to what you want. But if your idle adjuster screw is turned all the way in then it is still not right. You might want to check the butterfly screw to make sure someone else hadn't screwed it in to get it to idle up. Also make sure the cables aren't too tight to let the butterfly arm comes back all the way closed. Sometimes the butterfly screws can come loose and not the the butterfly close all the way. It is just barely supposed to be off the sides of the intake to prevent sticking. Did you try closing off the brake booster vacuum hose?

Let us know.

Russ

what were the results of your compression test?

do you still have high idle?

This is an 'oops' part on my fault. When it was mentioned about an idle control screw, I was looking at the one where the boot of the throttle cable rested (by the end of the throttle body) - I wasn't messing with the one that was IN the throttle body. Now that I've adjusted it, it's back down to 700 (after warming up, of course)

HIGH IDLE ('92 7mgte)
 

Hello!
I also have a high idle problem. I was trying to locate and pinpoint the "air screw" or "idle adjuster screw" being referred to in this thread. There's a hole (with metal plug) on top of the intake manifold near the hose connecting to the 3000 pipe. I thought it might be that, if the screw is under the plug. Not being sure I got it right, I was reluctant to remove the metal plug. Could someone pls help with picture or further description to locate this "idle adjuster screw"?
Also, how could I test or check if the ISC is bad? Is there a part, like a valve or something that can be replaced in the ISC without replacing the whole ISC assembly? I would really appreciate any further advice or help to fix the high idle. Thank you.