Ive been messing with my car for about a week now, trying to get it ready to take a smog test. Its a 92 firebird with a TBI motor. As far as i know, stock, 131,000 on the car, so im assuming the engine as well. I've been haveing some issues with trying to get the idle to smooth out. Ive done plugs, wires, cap, rotor, TPS, Inspected the IAC, checked for vacume leaks, O2. It has a rough idle, maybe a slight miss. not real bad, but still rough. When i start it hot, it will jump to 1,400 RPM, then right back down to about 750-800, and stabilize there. It seems kinda smooth then. As soon as i out it into gear, the idle drops to about 550-575, and becomes rougher. When i go back to neutral or park, the idle never comes back up, but stays down around 550, and rough. IF i restart it, it will idle at 750 or so again. Its very consistant at that. Also, i drove it for the first time today, about 10 miles, all sorts of load, and it ran great. I parked at a friends house for about an hour, and when i went to restart it, it didnt want to start, and when it did, it was surging from about 700 to 200, then stalled. I restarted it, had to give it gas to keep it running, and it woudlent take any throttle, and wouldent rev. After 10 seconds or so, it suddenly started running fine, and hasent acted up since. And help would be appriciated. I had my lap-to hooked up with WINALDL, and everything seemed to be right were it should be.

 

Anyone?

 

Did you only "inspect" the IAC, or did you actually reset the minimum air? What about TPS? Might also want to check the fuel pressure (with the regulator unplugged and see if it's reading 43 psi like it should. Also ensure the timing is where it needs to be (unplug the ESC connector before checking).

 

If you adjust the minimum air, you'll must adjust the TPS.

Fuel pressure can be between 40.5, and 47psi at zero vacuum.

The car has a "set timing connector" that must be disconnected when setting the base timing.

 

It's a TBI motor, fuel pressure should be 9-13 PSI.

Anyway, I agree with the above posts. Check anything and everything that you can. Check fuel pressure, check the timing, it should be at 0*. It might be worth it to remove and clean the IAC valve as well as the IAC passage in the TBI unit (unless that's what you meant by inspecting it). How does the injector spray look? It should be a fine conical shape with an occasional drip. How long has it been since the fuel filter has been changed?

Also, since you have access to a laptop and WinALDL, try taking some datalogs while the car's running rough, and post them here.

 

Havent checked the fuel pressure yet. Do you have to "T" into a line to do it? Since therse no port to check it? Fuel filter is on my to-buy list. Best i can see, injector spray looks ok. Yes, ive removed the IAC and checked the passages. It apears to be working ok, because i get fast idle, when its cold, then it idles down. The idle had been very stable, except for going into gear then back. I dont know if it relates, but the one time i had it surging and it stalled on me, i had just tryed to start it, it got like half a revolution, then lost all power becasue of a bad battery connection. I mean, lost all power, not dome light or anything. I tightened the battery cable, and it started, but was surging, and stalled. When i re-started it, it woudlent take any throttle, wouldent rev. I gave it lots of gas, and it finally started to run fine, and hasent done that since. I need to fix my ALDL cable, then i'll post a log. I cant drive the car right now, its blocked in, but i'll at least get a cold and a warm idle log.

 

Yes, you do. Most auto parts store sell or rent out a TBI fuel pressure tester (like the one linked below) that comes with a brass adapter. It bolts right in between the the metal fuel line and rubber fuel line in the driver's side engine compartment, and allows you to hook up a fuel pressure gauge to it.

http://www.actron.com/product_detail.php?pid=16175

 

SO, i got some WINALDL files. How do i attach them?

 

OK, here's a link to some files i put up on the web. A somewhat cold idle log, a warm idle log, and a key off log, to show the TPS values. http://home.ripway.com/2005-8/371083/index.html
The cool idle log is missing some data in the middle, as my cable fell out about half way though. The idle is definitly worse warm.

 

Can you post logs that are in calculated (i.e. not "raw") format?

 

I dont really know how. I tried PAnalyzer, but it wont work because my logs are in .TXT format. thats the way winaldl saved them. How do i get .CSV files so i can use panalyzer? I dont have excell.

 

Sorry, all i have is the text files with the raw data. I havent been able to figure out how to get anything else.

 

Hmm, I haven't used WinALDL in years... why not try Craig Moates' DOS-based software? You can download it here: http://www.moates.net/product_info.p...products_id=70

Another alternative would be TunerPro; that's what I use. I'm not sure if it's compatible with your ECM, though, as I have a '165 MAF-based car. Might not hurt to try: http://www.supportfitness.com/mark/tunerpro/

It's not really helping your car's problem, but we gotta start with good (easily understandable) logs .

What kind of Jeep do you have?

 

I have tunerpro Rt, but i need to make a cable. my single transistor cable for winaldl dosent work with it.
But here are the .CSV files.
http://home.ripway.com/2005-8/371083.../cool_idle.csv
http://home.ripway.com/2005-8/371083/8-4-05/key_on.csv
http://home.ripway.com/2005-8/371083.../warm_idle.csv

These work with performance analyzer, i could view the sensor data, converted.
Hope i can get this figured out. I really want to get the idle good before i try and get it smogged.
BTW, i have a 93 cherokee.

 

The car seems to run great other than the idle guality. It rev's nice. Drives fine. It will break the tires loose form a standing start, just by flooring it. Timing is set at 0 with the ESC disconected. IAC seems to work fine. It will adjust the idle when the a/c cycles on/off. Fast idle fine and idles down, when cold. Its just rough, shaky. Adjusted the valves today, not really any better. Still need to run a compression test. It dosent have any visible blow-by. Gonna try and get a fuel filter in it, test fuel pressor, and do a compression test. Just done feel like climbing back under there to pull the plugs i just put in. If you can tell me anything from my datalogs, that would be great. im still learning what it all means!
I guess the other question to ask, how smooth of an idle sould i expect from a TBI car?

 

Check to make sure your P.C.V. valve isn't clogged and make sure your air filter isn't clogged either. Another thing to check would be the intake manifold gasket and all the vacuum lines.

 

PCV is good. Runs the same air-cleaner on or off. Checked all the vacume lines multiple times, both visually, and with starting fluid. Tomarrow its getting a fuel filter and a TBI rebuild kit. Dont know that it will help,. but it needs to be done anyways.

 

You might want to pull the valve covers and use a dial indicator to check the camshaft lobes to see if maybe one of them has wore down. The intake gasket should be check as well as the rocker arms and pushrods too. I can't imagine the rocker arms or pushrods, but they're right on top of the cam lobes, so it's worth a cursory glance while you're there.

 

I'm hoping i may have found my problem. While pulling my TBI apart to rebuild it, i noticed that the injectors have different numbers on them. In researching, i found that i have one stock injector, and one 3.1L v-6 injector. I'm guessing that may be causeing it to run lean.

 

Well, replacing the injectors with some junkyard 305 injectors made a small improvement in idle quality. It was a more noticeable improvement in top end, how well it revs out. Way better. But the idle is still rough. I'm begining to wonder if its a operation related roughness or a vibration related one. Its very nice and smooth at about 900-1000 RPM, but rough when it drops down to 550ish. Its not a bouncy type of roughness, but more a smoth constant shake.

 

Check your motor and trans mounts. You might be on to something here.

 

Checked motor and tanny mounts. All look good. Did a compression and vacuum check. 140-145 every cylinder. Vacuum is about 15" at 550 rpm, and about 17" at 800 RPM. To summerize, So far, New GM O2, New TPS, TBI rebuilt, DIffernt injectors, IAC inspected, New cap, rotor, plugs wires, Tried differnt ingition module, tried differnt MAP, Tried differnt computer chip(out of a 89 caprice 5.0, just because im not sure if my computer is the right one) Checked the distributor for play, today checked the compression and vacuum. Now im not sure what the vacuum should be. The injectors is the only thing that helped a very little bit. It still idles rough.

 

When it's idling "rough," does the engine stay at a fairly stable speed (+/- 75 RPM)?

Nothing really jumped out in the logs.

Try checking the pins that plug into the MAP sensor; ensure that they are making a good connection. I had a MAF with a bad connector once... it threw off any logical diagnosis. Also make sure that the connectors on the back of the ECM are seated properly and that the pins are not oxidized.

 

The idle is stably, usually +/-50. when its cold, it will occsaionally fluctuate +/-100 or so. I guess connections is possible. But the map seems to read right, off and at idle. I might just try and get it smogged, and see what happens. All i really care about is that it passes. Then i have 2 years to start modding it.

 

I went ahead and replaced the IAC. Its holding about 750-800 RPM idle. before when you went into gear, the idle would drop to about 550-600, then stay there. It seems to be idling way better at 800 than at 550.

 

An idle speed of 800 RPM is still a bit high, especially with an unmodified engine. Does it still stay "stuck" at the lower RPM when you place it into gear? Hmm... can you take another datalog? At operating temperature: start the engine, let it run for a minute or two (until the idle stabilizes and the ECM enters closed loop), and shift into Drive. Sit like that for a few seconds, and shift back into Park. Note the time (on the scanner) that you do the shifting; I'd be curious to see how the IAC is operating under the circumstances.

The only thing (generally speaking) that is going to allow your RPMs to fluctuate is either the IAC or the throttle. Perhaps your "rough idle" is related to just too low of a target idle speed, but it's still unusual that the engine remains "stuck" at a certain RPM even after you shift into Park. It's entirely normal for it to drop in Drive, but the typical idle should return after shifted into Park or Neutral.

 

The idle speed is about 550-600 now, and consitent. The car passed smog great today, rough idle and all. I'm really beginning to wonder is maybe someone has put a cam in it and not changed the computer. it seems to pull way better in the upper RPM's, like 3-5000. But for now, its smogged, and that was my biggest worry.

 

Glad to hear everything went well with your smog check.

 

I"m having the same problem. Did you try a timing chain??

 

Didnt try anything internal in the engine. Since it passed smog fine, and the idle is consistant, im juts leaving it be for now.

 

Finally got it figured out. I finally broke down and bought a fuel pressure tester. I was getting almost 20 PSI!! The return line was plugged solid. I got the return line blown out, now it idles nice and smooth, and its noticeably quicker. I didint get around to checking the fuel pressure untill i got a SES light, code 45, rich O2 reading. Decided it was time to check the fuel pressure. Too much fuel really is a bad thing. Im really amazed it passed smog as good as it did.

 

I thought you had checked that already .

Glad to hear that it's fixed.

 

 

I never got around to checking it. didnt have a pressure tester, and the nearest parts place i could get to to see if they have a loner is 30 miles away!

 

That bites!

 

For those with similar symptoms, check the catalytic converter. My car had a rough idle and it died right when I pulled into the service bay at the dealer.

They checked it out and it turned out it was the cat and the fuel pressure was low, 6 PSI. Replace the cat and the fuel pump and never had a problem with rough idle again.

My symptoms were almost identical with what HillbillyJeeper has posted except that my idle had been rough for months.

I hope this helps somebody.

D.