Can You Help Me With Some Idle Problems?

Hey, guys. Some of you might remember me. I'm the guy that was going to grad school in San Diego that got his 1991 Talon stolen TWICE in six weeks. Well, I know I've been off of the map for a while. Sorry about that. Ever since I graduated, I've been in and out of the country, and ever since I went back to finish my studies, the Talon has been in storage. So, even though there are still a few problems, I've yet to start working on them. Well, that is, until now.

So, I pulled the car out. She hadn't been started in well over a year. Didn't matter, though. She started up with only a minimum of effort. However, I'm having idle problems. I was having this problem before I left, just never got around to fixing her. The biggest thing is that she's idling way too high. Somewhere around 2500 rpm all the time. She's supposed to idle a bit higher on start-up cuz of the cold idle switch. But, it's supposed to drop to around 800 rpm or so. She won't do that. Just stays around 2500 rpm. You guys got any ideas as to what to check on this?

Well, most of the time she stays at 2500. Sometimes, she'll go into a bit of an idle surge where it'll jump at a regular interval between about 1200 rpm and 2500 rpm. Weird!!

First off, let me tell you about the throttle body. The BISS is bottomed out. Can't screw it in anymore. Plus, the sensor that stops the throttle from falling all the way back (can't remember the name of it off the top of my head - has a single wire connector to it and screws sideways into the throttle body) is bottomed out, too. So, it's not a mechanical thing. Gotta be electrical, right?

Let me give you a little more background. Ever since I got the car back and resurrected her, I've had a few problems. I'm having turbo issues. My mechanic is convinced that the turbo is shot. It wasn't when they took it, but I guess that doesn't mean much. They raped everything else, so who knows what they did to the turbo. Also, I've got a constant hot that drains the battery overnight. So, gotta disconnect it or get a jump. My buddy's an electrician, and we're going to work on that this weekend. Not sure if my idle troubles are related to these other things, but I just wanted to give you an idea what we were looking at.

Other than these problems, my Talon is doing okay. She's not where she was before they took her, by any stretch of the imagination. But, she's doing good, all things considered. If you can give me some ideas as to what to check, I'd appreciate it.

Thanks for your time.
Jon

my car had a similiar problem.. i started it and the RPMs jumped up and down abnormally.. i had the plugs and wires changed and the problem ceased to exist after those episodes.

Do you have a logger?

* Check for any air leaks
* Check to see if the throttle cable is to tight, try loosing up the bracket on the back of the intake manifold.
* Test the TPS/ISC/EGR/Idle-Surge via Vfaq (http://www.vfaq.com/index-main.html)..
* Check base timing

Did you remember to ground the 2 terminals before adjusting the BISS? If you don't, the adjustment will never work.

http://www.vfaq.com/mods/BISS-1G.html

I would also pull your ECU and make sure the caps aren't leaking. It's a very common problem with 1g ECU's and causes all sorts of problems. You are going to have to pull it from the car and crack it open. Inspect if for damaged traces, swollen caps, burned chips, etc. Also, give it the "smell test".....Does it smell fishy?? If so, you need to have it repaired.

I would check the throttle cable first. Especially if its sitting at 2500 constantly. Redo the tension and adjust so the throttle plate is closed all the way. If you have cruise control, there may be a problem there too. The pedal could feel fine, however, the actual CC box and cable could be pulling or having an issue. The surge could be something else however. Just a thought.

Okay, thanks for all of the suggestions. I'll check on these ASAP.

Almost forgot to tell you. I did start a forum for this problem one time before. Forgot all about that since it's been so long since I put the car in storage. So, I didn't need to start a new one, but it's nice to get some fresh ideas.

One thing that I remember from before was that I started to lean towards the ISC being the problem. Not the motor itself, but for some reason, I don't think it's getting any voltage. Someone told me to test the plug. Can anyone give me any instructions on how to do this? It was also suggested to me that the part of the ECU that controls the ISC might be causing the problem and that the ECU might need to be replaced. Can this be tested with a test light or volt-meter? I'd hate to replace the ECU, then have that not be the problem.

As far as the ECU goes, it wouldn't surprise me at all if this turned out to be the problem. I replaced the ECU a while back, but that doesn't mean that the one that's in the car is the one I bought. Like I said, these guys did some weird stuff to my car while they had it. It wouldn't surprise me if the ECU in it now is the one that they had in their car (I'm convinced that whoever stole mine was after parts for their own). So, if you guys can let me know how to test this, I'll be forever grateful.

Thanks again for all of your help. I'll look into it soon.
Jon

I don't believe theres a quick way to test the ECU out. Only way I've seen it is when like a shop hooks up a computer to it and checks out all the sensors. Usually if the ECU is going bad, it'll be throwing bad numbers to the testing computer.

Quickest way is just to find someone who has the same car and swap out the ECUs and see if there's a difference. That's all I got.

It's not the BISS. I said that in my post that the BISS was bottomed out. And, I checked for leaks before putting it in storage. That's not the problem, either.

As for the Turbo, what we ultimately did was to cap the outlet, then put a pressure guage on that little vacuum outlet on the big outlet pipe. You know what I'm talking about? The black pipe that comes out of the turbo and hooks to the hose that runs to the intercooler. Anyway, when we'd rev up the engine, the pressure guage wouldn't go about 2 pounds. That's why he thought the turbo was shot.

Once again, it wouldn't surprise me if the turbo that's in it isn't mine. I can't say enough about the BS these guys did to the car. NOTHING would surprise me at this point. I just wish that I could work out these last few problems.

Thanks again.
Jon

As for the Turbo, what we ultimately did was to cap the outlet, then put a pressure guage on that little vacuum outlet on the big outlet pipe. You know what I'm talking about? The black pipe that comes out of the turbo and hooks to the hose that runs to the intercooler. Anyway, when we'd rev up the engine, the pressure guage wouldn't go about 2 pounds. That's why he thought the turbo was shot.

:twak: :rofl::lol:

I've posted extensively in the past about how the idle control system works, and common fixes and tests that can be done to rule things out. When I've got more time I'll see if I can search for them (maybe get them added to tech article forum too if they're any good). In the meantime, try a search, using my username if you like, something is bound to turn up.

Okay, got a couple more things to add and maybe some of you smart ones out there can help. First off, I wanted to say that the idle surge condition is much more common now. To be honest, it might even be more common than high idle condition I described before. It's a fast surge, too. I timed the surge for a minute and it surged up and down 72 times. Yes... seventy-two. One thing, though: I did over- and under-estimate the surge rpm. It surges between about 1100 rpm on the low side and 1600 rpm on the high side. So, it does drop some from the 2500 rpm that it has when the idle is high, but it doesn't get as low as it's supposed to be when it's jumping up and down.

One more very important development has come to light. The check engine light now comes on. And, usually, it stays on. I went and bought a LED and hooked it up to the diagnostic plug across the 1 and 12 pins. When the LED started firing, it gave me the same code over and over and over. The code in question was a 43. I looked into that code, and what I found was that it was "EGR (California Models only)". Is that what everyone else has? If so, I didn't know that my car had California emissions.

Anyway, allow me to apologize in advance for my ignorance, but would a bad EGR explain the funky idle conditions that I've been describing? I've never had to deal with a bad one, so I'm not really sure what the symptoms would be. For that matter, could that even explain my turbo problems? Let me know if you guys have got any input on this.

Thanks for your time... again!!
Jon

Once you stated where the rpm was sitting I started typing that the EGR valve is your problem. Then I seen you ran a CEL and got that also. I had a bad EGR on my car right now. Surge isn't that bad, and not as often, but its been doing it for a while.

Replace the EGR valve and solenoid. Then check ALL hoses and vacuum lines and piping in the whole EGR system. Make sure there are no blocks in the lines of build up. Mostly happens where the tube connects to the intake manifold. Clean all that crap out and replace the EGR and you should be good with that. It's amazing how much better the car will run, how much better your gas will be, and how much better peformance youll gain.

Any time idle is surging you are hitting the coasting fuel cut RPM limit. It is around 1600 rpm too IIRC. Essentially the car is trying to idle higher than 1600 rpm, but the ECU completely cuts fuel (coasting fuel cut) making it drop. When it clears the hysterisis limit it revs back up, and the cycle continues. Find the cause of the high idle (EGR, ISC, FIAV, BISS, vac leaks, throttle cable, lunar eclipse, etc) and you will likely have found the cause of the surging. With DSMlink you can raise the coasting FC limit, but that just gets you around the problem without really fixing it. There are times when it's necessary though.

Hey, guys. Sorry I've been out of the loop. Just found out that I'm leaving the country again. So, I've been scrambling to get all of my ducks in a row. This time, I'm going to Australia for a little over a month. Bummer, huh?! Anyway, this thread is going to have to get pushed to the back burner for now. I'll resume my quest when I get back.

Thanks for your patience.
Jon