I'm posting this again as it is frustrating as hell. I have a 3-4k rpm idle. It tends to change from 3-3.5, to 4, then to 3, then back.... it keeps doing this but occasionally stops and stays consistent for a while. I have checked and plugged all vac lines to make sure and it is not that. Any ideas? I'm about ready to sell the car...
If the throttle blade is truly closed, then you "do" have an air leak somewhere. Brake booster (and subsequent hoses, lines, filters), gaskets (Throttle body, intake manifold, etc), IAC stuck open... somewhere.
You might let it run and take an automotive stethoscope (or just a piece of vacuum hose to you ear) and go around the engine listening for a large hiss.
If the throttle blade is truly closed, then you "do" have an air leak somewhere. Brake booster (and subsequent hoses, lines, filters), gaskets (Throttle body, intake manifold, etc), IAC stuck open... somewhere.
You might let it run and take an automotive stethoscope (or just a piece of vacuum hose to you ear) and go around the engine listening for a large hiss.
Would the leak cause that high of a change in idle? I thought vac leaks only cause a change of a few hundred RPMs. Any idea where on the throttle body there could be a leak.
If you truly believe that it is a vacuum leak and not an electrical issue.... You could go about it the old fashion way.......be methodical and spray carb cleaner on one area at a time with the engine running.... when you find the leak the engine will tell you. If you use this method....do it when you first start the engine up and it's cold. If you need to stop and let the engine cool down that's alright...just remember where you stopped and start at that point when you fire it up again. I typically try not to spray carb cleaner on a hot engine unless I have a bag of marshmallows on hand with a fire extinguisher. It's old school but it works.....hey,we still dig holes with shovels don't we?!
[This message has been edited by MadProfessor8138 (edited 09-01-2015).]
Would the leak cause that high of a change in idle? I thought vac leaks only cause a change of a few hundred RPMs. Any idea where on the throttle body there could be a leak.
The reason I do not think it is a Vac leak is because when I run the engine and put a piece or cardboard or my hand over the TB opening, the engine dies. With a vac leak causing a 3k+ increase in RPM, I feel like the engine would run if the TB was blocked off, since it is closed at idle anyway. My thoughts were that air would be pulled in where the leak is and keep the engine running if the huge rpm jump was really due to a vac leak.
Originally posted by don297: The reason I do not think it is a Vac leak is because when I run the engine and put a piece or cardboard or my hand over the TB opening, the engine dies. With a vac leak causing a 3k+ increase in RPM, I feel like the engine would run if the TB was blocked off, since it is closed at idle anyway. My thoughts were that air would be pulled in where the leak is and keep the engine running if the huge rpm jump was really due to a vac leak.
Then the vacuum leak could still be between the throttle valve and where you were covering. Either the throttle valve itself or the Idle Air Control valve might not be closing all the way.
If your ETS (formerly CTS) went South it can signal that its -40* outside and signal the PCM to add a large amount of fuel. That will cause a very fast idle. Just experienced seeing this on a 3800 and the scan picked it up. Do a scan to confirm sensor readings. Unfortunately you cannot properly diagnose OBDII systems without the proper tools.
------------------ " THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Northstar TB, LS1 MAF, 3" Spintech/Hedman Exhaust, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, HP Tuners VCM Suite. "THE COLUSSUS" 87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H " ON THE LOOSE WITHOUT THE JUICE "
If your ETS (formerly CTS) went South it can signal that its -40* outside and signal the PCM to add a large amount of fuel. That will cause a very fast idle. Just experienced seeing this on a 3800 and the scan picked it up. Do a scan to confirm sensor readings. Unfortunately you cannot properly diagnose OBDII systems without the proper tools.
Tried TPS and IAC Still 3000rpm and searching. I guess its time to invest in a scan tool. Is there a cord I can buy that lets me scan the pcm and show results on my laptop? I was under the impression that OBDII tools dont work on the fiero since the only connector available is the ALDL?
Can anyone point me in the right direction for this?
May not help but I just had the same problem with my daughters 94 Buick 3800, it was a faulty TPS it didn't trip any codes but held the idle at 4000rpm.
Pull your IAC and look at the pintle. Is it fully extended? It should be. If it is fully retracted that is your problem. If you made the harness, and you have either the two greens or the two blues reversed that can cause the IAC to work in reverse. If you have one of the IAC wires not connected that will cause the IAC not to move.
A retracted pintle will have the engine idling faster. An extended pintle will cause the engine to idle slower.
If it is fully retracted you can extend it by hand. Pull back the spring and rotate it. When extending it, try it as you extend it little by little. Don't force the reinstallation with the pintle over extended since that will damage the IAC.
You can also test the IAC's motion by having someone turn the key on waiting and then turning the key off. The PCM should extend and then retract the pintle when the key is turned off. Note - the PCM can xtend the pintle to the point that it comes out of the IAC and goes flying. To keep that from happening you need to hold the IAC and block the pintle from over extending.
You can also test to see if the problem is coming from the IAC by taking it out, unplugging it so it doesn't move and sticking your finger in the IAC hole to block the air passages. Have someone else start the engine and fully cover the hole that has the vacumm on it inside the IAC hole. If you can make the engine idle down to less then 500 RPM then the problem is coming from the IAC in general. That being that the IAC isn't working, but not determining why the IAC isn't working.
Yes you can scan your 3800SC (assuming your PCM is 96+) with any OBD2 tool. Your harness should have the standard OBD2 diagnostic connector on it. Yes Fieros with OBD1 computers and OBD1 ALDL connectors need OBD1 scanners but if your Fiero now has an OBD2 computer in it, it should now also have an OBD2 diagnostic connector on it and it will scan with an OBD2 tool.
Bluetooth I like this scanner - http://www.amazon.com/Panlo...sr=8-3&keywords=obd2 - It will work with the free program Torque on your android device. It should work with a bluetooth enabled laptop but I haven't tried it.
Wired to a USB port laptop something like this should work - http://www.amazon.com/ScanT...-3&keywords=obd2+usb - but I haven't used it. I have older programs that have proprietary cables for laptop scanning that at the time cost much more than this one.
[This message has been edited by phonedawgz (edited 09-03-2015).]
Do Not trust Dash Tach. Always double check using ECM scan tool or Shop tach.
I have OE tach w/ problems that reads very high. Connect a scanner and scan reports 1000 rpm idle while Dash Tach says 1500. Highway? Scan says 2300 but dash is over 3000.
------------------ Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should. (Jurassic Park)
Scanned my engine and it is throwing a P0122 code. This is the Throttle/Pedal position sensor/curcuit A low. Now this doesn't make sense to me since I just replaced my TPS and IAC in an attempt to fix this issue? This makes this a wiring problem doesn't it? My harness was made by fiero flyer so I'm not sure how to diagnose wiring issues or what is going on with this. Any input?
I should have had you look at the actual value also - It should go from about 0.5v to 4.5v - from rest to WOT.
I could not get any voltage at the 5 volt wire. Does this mean the wiring is bad? How could the computer sense the throttle position being 0-100% open when it looks like it isn't getting any voltage. I used the method with the pins as well as removing the plug and stuck multi meter leads in the grey and black terminals on the plug. I could not read any voltage on my multi meter.
If you are getting a reading on the scanner, there must be some voltage on the gray wire.
Do you get the +5v on the gray wire on the MAP sensor? Again you should.
I have the multimeter set to 20 on the DC side, and again, I am getting no voltage across the TPS leads or the MAP leads. I get readings on the scanner of 0-100% for TPS and 14.1psi for MAP with the engine off. I dont know how I am not getting any voltage across the terminals when the sensors seem to be working.
