Motown

Have an 85 TPI that I have been trying to chase down a warm idle issue for weeks.

In cool the morning, or cool evening (75 degrees and cooler) the car runs great, no issues. When its above 80 degrees outside, and the engine warms up, I will pull up to a light and just before I come to a stop the car is jerking forward, like I am pumping the brakes, but faster. When Im stopped there is a definite lope in the idle. The tach corresponds with the loping and is very rhythmic. Not an erratic rough idle, but steady "miss"

Noticed today I started the engine cold and drove it about 15 minutes to a drive thru. Was idling in Drive smooth and all of a sudden, like a light switch, idle problem started like described above. Very distinctive miss.

In my searches, it seems my 85 has non multec injectors, not sure if pre multec injectors go bad too? Plugs and wires are all good. Someone mentioned a fuel tank pressure relief valve? LOTS (10 seconds) of hissing when I open the cap. Seems to run slightly better for a few minutes after I get gas and relieve the pressure, but might be my imagination.

The engine otherwise runs great. Very strong in all rpm ranges, roasts the tires easily. The engine has 101k. I dont plan on just throwing parts at this either.

Thank you for any help!

ruiterman

Have you checked the cap and rotor? I have an '85 TPI that overall ran pretty decent, had plenty of power as well, yet still ran a bit rough on some occasions. New plugs and wires helped, but didn't solve the issue comepletly.

After pulling the cap off the dizzy, it was obvious I needed a new rotor. The whole end of the rotor was gone. I don't know how the thing actually ran.

Just something to check. Good luck getting it going.

Ed

Motown

Thank you for your help. I will definitely check the cap and rotor for wear. Just by the looks of it, its been on there a while. Very dusty and dirty.

GreekItalianMan

I'm not sure it's the same but you're right I do have a similar issue. My dad said the hot weather also does it to. But, if there's old parts those are the culprit. Most likely cap and rotor and you might want to check your throttle body, tps, and iac too. I cleaned my thorttle body and it alleviated the problem somewhat but it's still there

Motown

Ruiterman, the cap and rotor look healthy, changed plugs with some fresh AC Delco's, wires look great, but my problem still persists.

Car still runs flawlessly when the engine is cold. Runs great longer when its cooler out (low 70s) but as soon as the engine gets warm enough, (15 minutes after starting cold) there will be a rythmic miss at idle and the tach is in synch with the miss. Tach needle vibes back and forth, not erratic, but rather, in tune with the miss.

When I accelerate when it does this, the whole car shakes until 2 grand but still accelerates well. My car is an 85, so it does not have Multec injectors and on top of that, ohm checking a few injectors resulted with 16.5 exactly.

Ive actually felt the "transition". Sitting in a drive thru, tach needle rock solid and then it will be like a switch somebody throws. All of a sudden it will start with its rythmic miss. And will stay there until the next morning.

Also when Im at a red light, creeping up in traffic, the car wants to "hop-hop-hop-hop forward" like somebody is pumping the brakes really fast.

Thats the best I can describe my problem without throwing up a video.

Someone please help me. I want to love this car. It looks beautiful but doesnt run beautiful.

z28romance

do you have a check engine light on? from what you described, it seems to me that once the ECM goes in to closed loop operation your having this issue. its very likely you have a failed part. once the car warms up, the computer goes from running on pre-programmed info over to running by using the sensors.

iggy1991

I agree wth z28romance. If theres no check engine light it could be anything. a volt/ohm meter would check alot of other sensors. faulty coolant temp sensor can cause some strange things like this to happen. its whatever sensor is not used in open loop versus closed loop. basically whatever sensors are not used when cold.

Motown

Thanks so much for the replies guys. Happening once going into closed loop makes sense because it happens so sudden once the engine warms up.

No check engine light comes on, but it does as a test when i turn the key on.

Ill do some digging around at various sensors ohm ranges such as the CTS and check them out. Ill update this thread once I find something.

Thanks again!

89shane350

iTrader: (1)

what was it?! my car is doing the exact same thing!

Motown

It started doing it weather the engine was cold or warm, and it didnt do it as much, sometimes for a whole day even at full operating temp, after a bottle of fuel injector cleaner.

I ordered some Bosch III injectors from Southbay and they will be going in this weekend. I will keep you posted.

Motown

Changed injectors and the car now barely idles.

skibum2100

What about the cold start injector, did you change it out as well?

ruiterman

Have you tried any datalogging programs or anything like that? It would be able to tell you running lean, running rich, live codes, closed loop/open loop, data values from each sensor, and plenty of other bits of information.

89shane350

iTrader: (1)

I bought a voltmeter from walmart for 12$ and tested the fuel injectors, there were all in spec, i check the tps and adjusted it to spec, it was off.

then i put in new plugs, wires, cap, and rotor.
next i check from trouble codes, the SES light wouldn't give me anything, i replaced the SES light bulb, it was burnt out. i got a code 36 that has been on for who knows how long. i replaced the maf burn off rely and reset the computer.

SES light is gone, idle is a hell of alot better and hasn't died yet!
but my cold idle is randomly LOW, sometimes reving it helps, sometimes it doesnt. and after warm up idle seems kinda high in park??

i was going to adjust the screw on the TB next, but i have the BBK 52mm TB and the screw adjustment on it sucks, it doesnt affect anything ether way, whys it even on their? so if thats the prob then im screwed because it cant be adjusted.

so next is fuel pressure test and vacuum test..

-shane

skibum2100

Hello

Congratulations on solving some key problems.

Don't count the injectors out; my injectors ohm checked okay, but 4 of 8 were dripping fuel.

The set screw should open the throttle blades, but be warned there is an entire procedure to messing with the idle set screw. Don't just turn it. The procedure is setting the minimum idle.

If the set screw is stripped, just pull it and tap the hole, then get another screw.

Hope this helps.

89shane350

iTrader: (1)

i still don't see how it works, it looks like the screw isn't long enough and doesn't touch the thing that moves the throttle, looks like just a screw in there hangin out! i tried the way to do it but the car wont stay started with the sensor thingy unplugged.... ill try it again at opperating temp on my next day off

89shane350

iTrader: (1)

mines doing it again, it wasnt because of the colder weather, fml... anything from you guys?

Motown

My problem has been FIXED.

Read this post, or the whole thread if you want.

https://www.thirdgen.org/forums/post...90-post51.html