1990 TPI with auto trans. The car keeps stalling. At first it only happened in reverse but now it's every time the car stops. It is not drivable. Every stop light I have to use two feet. Acceleration is amazing. I can easily throw the passengers head against the back of the seat. It's just idling that is an issue. It happened even in park after I gave it a rev. The IAC is less than a year old. There are no codes. What are some other things I can check.

 

Vacuum leaks, plug wires not grounding against anything or burnt, TPS is set correctly and loose intake manifold are a few.

Before we can help you, give us ALL the details. Car mileage, running rough, did it start after last fillup, when did it first start(was it after working on the car), you can't say it won't idle and expect any real help.

 

118k miles on the car. cap & rotor, plugs, wires, injectors, o2 sensor, done about a year or two ago (2k miles ago?). Car doesn't run ruff. For the passed 6 months or so it only stalled in reverse. The problem is getting worse and worse. Today it started stalling at every stop light. If I rev in park it stalls half the time. It doesn't matter if it's a cold start or after it stalls the car always starts up right away. On the tach I have a line between 500 and 1000 rpm I'm guessing that's 750rpm? In park it is a little above that line (800rpm?) and in gear it's just a little below it (700rpm?). I can easily smoke the tires. Upper rpms seem completely unaffected. Anything else?

 

Found this in ALLDATA:

You can also enter "Field Service Mode" by jumping ALDL terminal a to b.

NOTE: If the minimum idle speed is adjusted too high, the IAC pintle will constantly seat in the throttle body, and may cause damage to the IAC valve. If the minimum idle speed is adjusted too low, the vehicle may not start in cold weather, or may stall during warm-up.

ADJUSTMENT:



Block the drive wheels and apply the parking brake.
Connect a scan tool to the ALDL connector.
Turn the ignition on.
Select TPS on the scan tool and adjust the TPS voltage (see ELECTRICAL SPECIFICATIONS under SPECIFICATIONS ).
Select "Field Service Mode" to seat the IAC pintle. After 45 seconds, disconnect the IAC connector and exit the "Field Service Mode".
Disconnect the distributor set timing connector.
Place the transmission in Park (A/T) or Neutral (M/T). Start the engine and run until operating temperature and closed loop conditions have been met.
Select "Engine RPM" on the scan tool.
Adjust idle speed if not within specifications.
Turn the ignition off.
Connect IAC and set timing connectors.
Turn ignition on and recheck TPS voltage.
Reset the IAC pintle position by doing the following: ^Depress the accelerator pedal slightly, start and run the engine for five seconds. ^Turn the ignition off for ten seconds, then start the engine and check for proper idle operation.
Disconnect the scan tool.

 

Take the air induction hose off the throttle body and take a look inside the throttle body. You might find it's pretty dirty and blackened around the throttle plates. If so get spray can of thottle body cleaner.

It sounds like this could be your problem.... maybe not, but worth checking. Your car runs fine past idle. Stalls at idle. It could be something as simple as dirty throttle plates that's not letting enough air to pass by them and keeping your car idling properly.

 

Check your PCV valve, too. You'd be surprised how often it's neglected at tune-up time and a clogged one can cause erratic idle like your car is exhibiting, too.

 

just did it. A little bit of crud cleaned. problem still there

 

I went through every inch of vacuum hose in the car. Replaced one that was cracked. plug wires are neat and not burnt or anything. problem still there. How do i test the TPS?

 

i'll double check it next

If anyone has any other suggestions that doesn't involve a scan tool i'm all ears. I've got the entire day to play with the car.

 

I have a 1991 corvette with the same problem, the fix was a complete flush of the full injector and TPI cleaning, also replaced the EGR valve and cleaned the IAC and finally check your fuel pump to ensure is working properly, I replaced my with a high pressure one, after resetting base idle and resetting the IAC at 0.54 volt the Corvette runs great and idle without problems. I will suggest first to test every component before replacing it, sometimes the ECM will not give a problem code it will require troubleshooting such as the fuel filter being clog it will impair performance and create problems. many factors cause idling issues in a corvette (Coolant TEMP sensor, the O2 sensor, TPS, IAC, low fuel pressure, injectors leaking down or bad, bad fuel, clog catalytic converter, intake gasket leaking, vacuum leaks, MAP sensor and ignition timing, spark plugs and wiring ), these are some of the things you need to look into. I know is a lot of things but if one is malfunctioning you will have idle and performance problems. Lets know what is you outcome.

 

What ever the problem is, it's getting worse. It's stalling out in park just sitting in the driveway. No loss of performance what so ever. I can still smoke the tires without problems.

I took the throttle body off and gave it a good cleaning. IAC was very clean already but I went in there with a Q-tip any way.

PCV value was clean. I put my finger over it and I have suction.

I'm working blind without a scanner. I guess I'm going to have to give in. Where is the cheapest place to get a ALDL to usb cable?

 

Bare with me here as this might be long. When I bought my 85 five years ago it felt like it wanted to stall. The first thing I bought was a GM 1985 Shop Manual. I understand old cars without computers. The 85, I didn't understand any of it's sensors and what nots.

In the shop manual I found what's called the Throttle Position Sensor (TPS). It said, hook up a multimeter (I made little jumper wires on the TPS plug and plugged it back in the TPS). Start the car and read the volts on the meter. Unfortunately I can't remember what it was supposed to be and I can't find it in the shop manual. I'll keep looking though after this post. I think it was 4.9 to 5.4 volts, something like that. What you do is loosen the 2 screws holding the TPS on (on the passenger side of the throttle body). Turn it left and right until you get that proper volt reading on your meter. These meters by the way are cheap, under 10 bucks at most any store.

My brother bought an 85 about oh 3 years ago with 7,333 miles on it, yep, 7,333 miles. His 85 would stall at traffic lights and well everywhere when he'd have the AC on and the car was idling. One day at his house he told me about this so I adjusted his TPS by ear. I loosened the 2 screws and rocked the black plastic TPS sensor back and forth. One way the idle would get worse and the other way it got better. I didn't have my multimeter of course, but I guess I got it pretty good just buy the sound of the engine idling. I also had him put it in drive and with the AC on. This was about a year ago and he hasn't had a stall problem since. I guess I hit it lucky by adjusting his TPS by ear and understood what I was doing as I went through it with my 85.

I also read in the book this morning about the Idle Air Control Valve (IAC). This electrical thing is on the same side as the TPS. This IAC is in between the water outlets below the throttle body. It's a screw in thing that I guess measures water temperatures and sends this info to the computer. What else I just read was, it must not be soaked in any liquid cleaner or solvent, as damage may result. This is another possibility with you engine not wanting to hold it's idle.

Maybe give the 2 screws a loosen and rock the TPS back and forth. You just might have a smile on your face when you hear the engine idling a lot better and holding an idle. I did when I did my brothers.

Oh, stop smoking your tires. LOL That can get expensive.

 

on a 1990 is not adjustable. It locates itself by a little slot that fits over the TB tab.
It sounds like it could be the culprit or the IAC not working properly.

If you turn the AC on it should regulate the air in the TB and bump up the idle speed of the motor.

I hope you find out what is causing your problem.

Also: If this car is new to you, make sure that your PO didn't remove the light bulb on the diagnostic display for the check engine code. It will light up as a self check on initial start up when you turn the key and stay on for 2 seconds. If yours does not do this your bulb is missing or burned out.

 

I favor the method of adjust the IAC by setting it to about 20 counts. The TPS is adjustable. You just have to slot the screw holes.

 

Yep, not adjustable. I couldn't find my digital volt meter but I did find my analog. TPS is reading .5v no throttle and 4v with the butterflys completely opened. I slowly opened it and the voltage steadily got higher. No jumps or anything like that.

Check engine light works. I did the paperclip thing and only get the normal code 12 thing. Nothing else.

 

I'd lend you my scantool but we are too far away. Get a simple one like an Auto X-ray. With that you can read TPS and IAC counts among many other things.

 

You think one of those hand held scanners would be better or should I just buy a aldl to usb wire? I would get what ever was cheapest but they seem to be priced about the same. This is my only car with a 12pin OBD1 so I doubt it will get much use. My 95 has that mutant OBD1 computer with OBD2 connector. All the other cars in the family are OBD2.

 

My Auto X-ray does all that. Yes, it is nicer to have it in the car but here is the deal. You don't really need it every day. OTOH, the scanner is portable to the other cars.

 

I didn't know 1990s had a non adjustable TPS, learn something new everyday huh. Anyway, I tried in helping figure out the problem. Sorry I wasn't of help with my guess. Plus reading up above I remembered adjusting mine with the meter and with the engine off, key on. None of that matters anyhow as mine and my brothers are 85s and not later models.

 

no big deal. it was worth a try. i didn't know it was non adjustable either until i went out and took a look at it and it's my car