dirtymike77

My 84 crossfire wants to idle around 400-500 and keeps stalling until it's warmed up. is there any simple way to just bump up the idle a little?

DUB

YES and NO.

BUT...

More SPECIFIC information needed from you.

Please ANSWER all questions...due to they are important.

I am assuming this engine is still factory. (yes or no)

Roughly...How many miles on it?

Automatic or 4+3 manual???

The last time you did a good ignition tune up????

REALLY IMPORTANT!!! Is your Corvette stored in a garage or is it out in the elements???

I am NOT judging you...but what grade of fuel do you use??? and is it a name brand or off name stuff???

When you start it and get it running the FIRST time in that day. What is the RPM????

And at this RPM...how is it running??? 'hunting' or going up and down in RPM, steady rpm, rough idle. etc.

IF the RPM is high when you FIRST start it 1200-1350)...how long does it take to begin to idle down to 700 RPM...IF it does it at all.

Just raising your idle may be hiding a much large problem that may need to be addressed.

I know you may not wan to hear this...but it is what it is. And if specific 'things' are not in line and correct...turning screws to raise things can make it so your idle is higher...but it can cause other problems.

The engine should be idling at 500 IN GEAR( automatic)...when it is at operating temp....and roughly 700 RPM in PARK or Neutral (automatic)

Timing issues...EGR valve issues, vacuum leaks, throttle body shafts being worn out, coolant temp sensor issues, MAP sensor issues, Bad ECM (computer)...either grounds going to it or power going to it. Throttle position sensor not adjusted correctly (possible)...Oxygen sensor being bad or the wire has melted to the exhaust or is grounding out on something metal somewhere...and low fuel pressure. ANY exhaust leaks at the engine and OR in front of the Oxygen sensor, plugged or restricted Catalytic converter....but that usually will restrict the power the engine can produce....and can glow cherry red.

A voltmeter or scanner would help.

DUB

garryowen

good explanation dub

posting so i can follow thread

fredd1

Check if you're ALCL (OBD-1 type connector) indicates a code 22 for the low idle. If so, check the voltage signal at the TPS when in idle to see if it reads 0.52-0.56 vdc. There are three wires attached to the TPS, black-grnd., grey-5vdc., drk.blue-0.54vdc (@ idle). Check for proper ground and the 5v level first, then check for the low signal voltage. If you're not getting about 0.54vdc at idle you probably need a new TPS.

Rohn

My CF TPS was adjustable.... You can buikld a simple jumper to verify V. Key on engine off.

did someone remove the caps that allow idle adjust?

DUB

YES...the TPS (throttle position sensor) is adjustable. So just because it is not at the .54 volts or .58 volts ..(which is where I set them at)...does not mean they are bad. NOW...if you can not adjust it...then that is something entirely different.

The problem with turning the rear throttle body idle screw...may work...and may not. Like I wrote above...many other issues to consider...first.

DUB

swamp21

Ok, it's an old thread, but currently relevant to me except my idle is too fast. I'm sorting out my '84 C4 (86k miles, 4+3 trans) to which I've done the following: ported intake manifold, removed EGR, 1.6 rockers, '85 fuel pump, pressure set to 13ish, had throttle bodies rebuilt & shafts bushed and injectors cleaned, new coolant temp sensor, new spark plugs, base timing set at 8 degrees BTDC, cut a hole in the front shroud to allow cold air into the hood intake. TPS at no throttle is .53V as read through the ALCL. When checking over ALCL all sensors seem to be responding, although I'm not familiar enough with "reasonable" measurements to be confident they all make sense. The guy who did the TB's tested IAC's and TPS and found acceptable operation. Running non-ethanol 90 octane. Overall, car is running well, no check engine light. But I can't get the idle speed down. Wants to hang out around 1300ish. I'm figuring I have a vac leak somewhere but sure can't find it.

Anyway I'm picking away at it but if there's any pearls of wisdom out there to share, please do!

Thanks,
Steve

DUB

Steve,

I literally only have minute or so and will not get back to this due to being so busy but I will throw these concerns at you. Call me if you need to. 704 -394-5150
1.) Need to know the MAP sensor voltage due to it can tell you if you have a vacuum leak. You are looking for about 1.2 to 1.4 volts if my memory serves me correctly.
2.) IMPORTANT. How were the throttle bodies balanced???? Some use a sheet of paper a but I prefer to use the manometer and do it like GM outlines due to the manometer is very precise. THIS IS AN IMPORTANT STEP that should NOT be overlooked. Having the correct IAC passage plugs and manometer does wonders and I never assume that the way is WAS set is what it will be when I get done with it.
3.) Was the intake manifold top plate gasket replaced. I have seen them so dry and hard they crack into pieces. I have replaced more of them than I care to remember. Correct torque values are also important and not just tightening things to what "they' think is what will work.
4.) IF the car has not been driven and is still sitting there after all of the work has been completed. Keep in mind the IAC's need to re-learn so it must be driven above 35MPH.
5.) Lastly I have written this MANY times. ASSUMING that the notch on your harmonic balancer is in the correct position for timing can be a problem unless you verify it. I have encountered this notch be as far off as 2 inches. I have made a piston stop tool out of an old spark plug and threaded rod. I install it in the spark plug hole for NUMBER ONE cylinder and turn the engine manually until I make contact with the stop tool. Mark the balancer and then rotate it manfully the other direction until the piston hits the stop toll again and make another mark on the balancer. The distance between the two marks is TOP DEAD CENTER

Sometimes I thread the rod in or out so when I mark the balancer at the '0" mark on the timing tab. When I am done the two marks are close together.

DUB

Buccaneer

DUB! Is that really you? Where have you been for so long? Nice to see you back. Sorry for the highjack to OP.

swamp21

DUB - thanks much for your comments. Through tracking down some minor leaks, replacing MAP and O2 sensors, working through (most of) the idle setting procedure the car will now idle at a reasonable level. The only thing, it takes a little while to get down there. Maybe like 20 seconds to gradually come down? If I punch the accelerator, it'll usually come down faster. Not sure what that's all about, it's like the IAC's are taking their time, but at least it's tolerable now. I did not attempt to balance the TB's - the car was my dad's as original owner, I know it hadn't been messed with and the weld on the synch adjustment screw was still intact. It's probably something I can check with the carb synchronizer I use on my motorcycles but guess I figured it shouldn't/couldn't be far off.

I am a bit confused about the IAC's setting themselves once the car is going 35+, although I was aware of that requirement. But what are they setting themselves to, at that speed? Certainly not idle!

That's very interesting & disturbing about the harmonic balancer reference line, I was assuming you could use that as gospel. For whatever it's worth the car is running great now, smooth and happily running up to 5k+. It is running a bit hotter than it used to. Maybe that's just the result of removing EGR?

DUB

YES it is me. I am really super busy and have no time due to a special project I am trying to complete.

swamp21,

To answer your question about IAC's and how they work. It is my understanding that the IAC is a way GM used to control and air at different throttle angles. It is....as I have been told....a controlled vacuum leak. Similar but yet not exactly the same as your idle mixture screws on a carburetor.

Keep in mind the engine is computer controlled and when driving the car above 35 MPH the ECM is adjusting the IAC's for the engine to run the best it can by taking into account other inputs to allow this adjustment to be viable. SO,,,,when the engine is now idling due to TPS voltage is telling the ECM it is at idle ....the IAC's will adjust accordingly.

If the point of the IAC is damaged or built up with crud...then it cannot seat correctly and cause issues.

Also...I have found that the ECM is junk and even though the engine is running it needs to be replaced with a GOOD ONE and also replace the prom so the engine will run correctly. These computers were NOT designed to last forever. I do not buy them from an auto parts store I only get mine from one place. NUMEROUS times I have worked on cars like yours that has a glitch and finally put in a good ECM and chip and it fixed the glitch.....even though all parameters on my scanner looked good while it was idling or running down the road.

Keep in mind that your ECM....compared to todays ECM's..... is quite prehistoric in their speed and what they can process and do. Expecting it to do things instantly is just not going to happen all the time.

So knowing that your throttle bodies were set to an NEW engine. Logic would dictate that even IF the throttle bodies were re-bushed and freshened up. The setting on them may need to change due to the engine has age on it....or even if it were a freshly rebuilt engine.

As for the tool you may use to set your throttle bodies I cannot not comment on it and I ONLY use a manometer as previously stated.

I cannot comment on what you mean by " running a bit hotter". Not knowing what the engine was running coolant temp before and what it is now. I doubt the EGR had anything to do with it due to the EGR is taking exhaust and running it back through and burning it again. Have you used a coolant system pressure tester and checked to make sure your coolant system holds about 15PSI for about ten minutes???? Your coolant system is s CLOSED system and MUST hold pressure and this is not debatable. Also making sure you have your lower front air dam INTACT and not removed aids greatly. Blocked radiator cooling fins internally in the radiator, bad coolant, block drains that have never been removed to clean out the engine block of crud, bad radiator cap can be culprits.

DUB

swamp21

DUB, thanks again for your extensive comments. A few things...

I have a pretty good understanding of the IAC function and basic operation, but I thought they were pretty much irrelevant off idle, the air is coming through the TB butterflies - not the IAC leak holes, so that's why I don't get why driving them at 35+ mph resets them. All the sensor readings don't seem particularly relevant at that speed as would pertain to a proper setting of the IAC's in it's relevant zone.

Contrary to some other posts I've read, when I jumper pins A & B on the ALCL, my IAC's do not extend to their full out position, they just keep cycling back and forth between some limits whose origins are not understood by me.

Re: your ECM comments - are you saying possibly my original one is a bit suspect, and I should consider replacing it? Are there better (e.g. faster/more current technology) options that could work?

My thought on the the TB sync using my bike synchronizer was just because I don't have a manometer. I can look at the 2 TB's at the same time, although it will be a relative measurement to each other, not an absolute.

The comment on running a little hotter - before my mods, the thing would pretty much stay at 195 on steady cruising - now, it's seems to be 5-10 degrees hotter. And when in stop and go, it raises very fast. I haven't had it overheat yet but the cooling fan doesn't kick on until 225-230 and it makes me a bit nervous and seems unnecessarily hot. I know they were set up to run hot, but it seems a bit much. I'm gonna put in a 180 thermo and a lower coolant temp switch to cool it down a little. I had advanced the base timing a couple degrees, maybe that did it. I do need to check the radiator crud status and probably replace the cap on principle.

DUB

Because it is written in a GM service manuals that whenever dealing with IAC's. The procedure to how you need to do prior steps BEFORE disconnecting them and removing them is outlined specifically. And...any time they have been messed with and the battery disconnected it is common knowledge with mechanics that driving the car allows the ECM to set parameters.

I know when I attach my scanner I can read the IAC value and it is usually (if my memory serves me correctly) the value goes to140or it may go to 160. But nonetheless it goes to the maximum value. Then when I crank the engine and get it running I can see the IAC value change to aid in maintaining a smooth idle.


I believe I have read that some people here on the forum installed a computer with higher processing speed but I personally have not done it. I do not see the need due to IF all is correct. The Cross-Fire engine runs really good and I have customers who can testify to that. I am NOT telling you to replace your ECM. I was just saying that it can be an issue if you feel you are chasing your tail and cannot get a specific 'bug' worked out in how the engine runs. But in the same breath....IF you do not follow specific outlined procedures and assume the ECM is the problem due to not checking things...then the outcome MAY NOT be what you hope for.

As I have mentioned before. Some people use a strip of paper or thin feeler gauge to set the throttle bodies. If it works or them...GREAT. BUT...GM has specifically outlined how to do this and by using a manometer and I can tell you this. FROM EXPERIENCE: I have had to install and balance some of the bored out throttle bodies. Those throttle bodies DID NOT have the vacuum port I need to use my manometer due to it was plugged off. And attempting to get them set correctly using strip of paper was the biggest pain in my backside. I did not like it and it actually took me longer to try to get things right, WHY?? Because when using manometer....obtaining the 6" of water is so easy and the adjustments are so precise to do this it makes the job go as designed.

Installing a 180 degree thermostat is NOT...repeat NOT going to change your running temps at all. So the sitting still coolant temps are still going to get to the 225 range.

I KNOW that most people begin to freak out when the coolant temps get to the point where the cooling fan comes on at roughly 226-228 degrees Fahrenheit. but honestly I do not even bat an eye at it any longer. I worry when the temps get MUCH higher. Because the cars equipped with the secondary cooling fan. I believe that fan comes on at 256 degrees F.
So if the cooling fan is ON and the temps keep rising and get to about 240. THAT is when I am paying careful attention to what is going on ...BECAUSE...I also have to take into account IF the coolant temp sensor is not failing and giving me a false value. So sometimes I have to STOP...shut down the engine...let it cool and install my racing temp gauge and check it again to verify if it is really getting that hot or if it is a faulty sender or some other issue in the cooling system is causing this issue.

I am sure are aware of this but I will write this that when replacing sensors and important parts on your car. It is WISE not to assume that they are all the same due to they are not and installing a cheaper non-OEM part can cause for problem. I only install aftermarket sensors when OEM is no longer available and I have no choice. WHY? because I have experienced it and have seen that the life of the part or how it works correctly often times can differ greatly from what it needs to do..

Best of luck to you and I am signing off on this. You have my number if you need to talk about this.

DUB

GregMartin

Should make this a “sticky”. I feel like I’ve given the same advice over one over again.