The car runs well except sometimes when I am driving it hard when coming to a stop the RPM's will drop and the car will die. Now it has developed the problem that it will not start unless I press the throttle, and if I start it, and release the throttle, it will die. If I hold the throttle down and keep it at about 1500 RPM's for a short while, then it seems to be ok.
The car now starts, but has developed a different problem that I believe is related. When I am driving the car and I put the clutch in the RPM's drop really fast and the car wants to die, unless I press the gas. If slowly get the car to stop and ease the RPM's down slowly, it will idle but it takes some work.
Your check engine light does function but normally is off?
So the fact that the ECM is opening up the IAC passage to allow the engine to idle is showing that the IAC is working. The ECM attempts to control the idle speed when it sees the throttle closed. It knows the throttle is closed by looking at the TPS (Throttle Position Sensor). So if your TPS isn't working, or is adjusted off the ECM may be thinking the throttle isn't at rest and it won't be looking to adjust the idle speed
The ECM also looks at the VSS and doesn't look to idle the engine to the normal target idle speed unless the vehicle isn't moving. A normally operating Fiero ECM will have the engine idling faster but it also doesn't try to adjust the idle speed when the car is rolling but then it slows the idle speed down when the car comes to a stop.
No VSS signal will cause the ECM to always think the car isn't moving. Thus you are driving down the road and the ECM thinking the car is standing still closes down the IAC passage trying to get the engine to idle at the correct speed. But if you are rolling to a stop the engine is running too fast for the ECM and the ECM gets the IAC way closed down. Then you push in the clutch and the engine idles really slow or even dies. If you keep the engine running with the gas pedal the ECM sees the too slow idle speed and then opens up the IAC passage.
Both a bad TPS and a nonexistent VSS signal SHOULD cause a check engine light if the check engine light works.
[This message has been edited by phonedawgz (edited 07-13-2014).]
The TPS is also used to sense larger changes in the throttle position and when the ECM sees that it activates fuel enrichment programming (think accelerator pump)
Also when cranking if the TPS is over something like 80% the ECM goes into cranking "flood" mode and reduces the amount of gas being injected to a minimal amount.
That's about all the TPS is used for. The ECM uses the MAP as the main sensor to determine how much fuel to inject, not the TPS.
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[This message has been edited by phonedawgz (edited 07-12-2014).]
Ok, great info. VSS is working fine and ran to the ECM for the 7730. No SES codes, and ECM is working correctly.
I am throw parts at things guy to test, don't worry, I don't run to the auto parts store, I have a bunch of Fiero's laying around, so I just swap parts to test. Quick and easy testing before digging deeper.
So I replaced the IAC, no change.
Replaced the TPS, and now the car idles. Dips a little low, like 700 RPM's when I come to a stop. Only time I was able to get the car to die, is if I ran the A/C then it died when I came to a stop.
Usually ECMs will keep the RPMs higher when the vehicle is moving and then the drop it to the target idle when the vehicle speed reaches below 7 mph(ish).
Any chance you have an idea how your ECM is programmed? Are you running a stock chip?
Did this work fine after the 7730 swap and then had problems later or is this from the 7730 swap?
With the car just idling what happens when you turn the A/C on? An overcharged A/C can put a significant load on an engine.
[This message has been edited by phonedawgz (edited 07-13-2014).]
Ok, car was idling fine in the driveway, I pulled out, and drove to the stop sign, and the car died. I believe I used the right definition file, but I emailed Darth (Ryan - I bought the chip from him) to be sure. I recorded the short trip using Tunerpro RT. The file is available here -
Ok, I found that idle screw did not have a cap on it, so at some point, it must have been moved. I adjusted it until the car would idle, and fingers crossed it idles and doesn't die, even with the air conditioning running.
