Hello,

I have a 1982 Trans Am which idles very rough, it will start fine but never idle smooth, it drives fine, it also does not have its cold idle of 1500 RPMs anymore. The check engine light never comes on when I turn the key or jump the diag connectors. In a sense there is no check engine light at all. The idle is about 600 cold and 600 hot. It was running fine prior to this bad behavior.

When I unplug the IACs nothing changes, it continues to idle rough. When I unplug the ECM 10A fuse the car idles worse and will stall if you touch the gas.

Thanks,

Morgan

 

The Check Engine light might be as simple as a bad bulb. Has it ever worked since you've owned your T/A? I'm surprised a CFI car would run at all with the ECM fuse pulled. I know cranking circuit is separate and a car will turn over but not start but in run the ECM controls fuel and ignition in run. Have you checked all the harness connections and grounds? You could have a problem with just the PROM or the ECM itself. If you don't have access to a code reader/scanner then a parts store like Advance or Autozone generally will do it for free.

One thing I've found CFI cars don't like are vacuum leaks. Have you replaced all the vacuum lines recently (also the manifold lid gasket - check the retainer bolts)? Worn TBI throttle shafts will cause erratic idle and surging while running but this isn't a sudden occurence issue (it's one that gradually happens). My '83 would do this but it might not be your only problem. The EGR valve could have carbon build up. The same could be said for the IACs -have you taken them out and cleaned the passage and checked the plunger isn't binding?

I hope this is a help for you to start with.

 

All vacuum is good. The cel has never worked. I unplugged the tps map and both iacs and the cya plugged it back in and it ran great. Well it started running rough again so I wonder if something is sticking or is malfunctioning. It has 39k original miles.

Thanks for your help!

 

The cel has never worked. I unplugged the map iacs and tps and cts and replugged and it ran great. The vacuum is good. It has 39k miles. After driving it all day parking it and returning to drive it's rough again.

Thanks for your help!

 

I would think given the CEL has never worked since you've owned her either the bulb is bad or removed. Some did this if they couldn't clear the trouble code(s) or was selling. Check this and ,if just a bulb, you have a way to check for codes without a scanner. I would still have her scanned to have a starting point for troubleshooting.

Since unplugging the sensors had her running better then it seems to be an intermittent problem. As I stated before the IAC passages could have carbon build up, the TPS could be out of adjustment, you could have a slow or bad CTS and then it could be as simple as a loose harness connection or ground.

And you are most welcome. I've learned about my CFI by reading and asking questions. If more time had been taken when they were new the syatem would have less of a bad reputation reliability wise. On the performance side the design was handicapped from the start.

 

Okay update: The CEL bulb was burned out, that sorta worries me that it was on forever. Anyway the code stored is 44 lean exhaust. The CTS connecter was about to fall off, or the wiring was, so I replaced the connector and CTS. Also I got a manometer to check the TBI sync, it is a digital version and I should be able to adjust using that. I do however believe something is wrong beyond being out of sync, I would think the out of sync situation could generate a CEL, all though the CEL lit up on the freeway.

I also lost the radio display at the same time all of this started, and the fuses are fine.

The car has always had a cold idle of 1500 RPM, however that disappeared, as well as the 1500 spike on hot starts, I believe the answer lies in what ever sends the message to rev higher when cold and spike when hot and idle in general.

Thanks again!

I know I can fix this, if I can keep my 84 380sl running, this car should be easier!

 

Another update: I adjusted the tps to 1 volt it was at 1.98. I built a manometer because my digital version did not work. Anyway I balanced the tbis and even though the iacs don't appear to work right the idle is pretty smooth.

Not sure what to do next.

 

If you don't think the IACs are working, I would go to that next.

 

I agree if you don't think the IACs are working correctly I would look at them next. The plunger shafts on mine were gummed up and the TBI ports had carbon buildup. All that had to be done was a good cleaning and they work correctly. These affect/control idle and if not working can cause a rich or lean condition (depending on plunger position). I used 0000 steel wool on the plungers and a bottle brush to clean the ports.

 

Correct it is the IACs. I removed and cleaned them and magically my cold idle returned. I double checked the balance of the TBIs and they are good. I can't imagine the crossfire set up being such a bad idea, I mean if the intake leak, and the shafts wear out, all that can be fixed. But then again I did not have those problems yet, I have 39k miles on my car.

It runs great, its pretty quick off the line and sounds great.

Thanks for your help!

 

That's great to hear you've solved the idle problem. You did it the best way taking one step at a time and not just throwing parts at it hoping that will solve the problem.

The CFI setup is great for low end up to 4K RPM. If you want her to breath better port mathing the lower manifold and cleaning up the intake really makes a difference. There are a couple other choices to replace the intake also. The stock TBIs can be machined to accept 2" butterflies and these will still work on the stock intake lid. Then the exhaust side needs attention as the LU5 shares it with the LG4. You have a choice of either using L69 (or L98) exhaust manifolds,y-pipe,4 bolt cat or headers and a cat back system.

 

I think I am going to just keep it all original, I mean with less than 39k miles its probably best to leave it alone, it does run very very good after all the advice, in fact its impressive how good it runs, I couldn't be happier with this car for the price.

 

how is the car running?

 

It runs well I also adjusted the fuel pressure to 14lbs and that made it very smooth.

 

how did you adjust your fuel pressures

 

Remove the rear tbi regulator and set to max then back off till 14lbs. It actually was at 10 lbs so I put 4 more. It's spring loaded. I will find a link later for you.

 

thanks

 

Here you go.
http://www.fl-thirdgen.org/tbiafpr.html

 

thanks