This is a stock 2.8 86 GT 5spd. Only non-stock part is the accel coil. (yellow one)

Tuesday after work, i stopped in the auto parts store cause i was about a qt low on oil. Put in the qt and drove off. (it was lightly raining) I got about 5-7 miles up the street and the car went dead. I figured it was the ICM. So i put one in from a motor that is sitting around that ran great before it was pulled. Car started right up with no hesitation. The next day i started it up and started to go to work. On my way to work i notice it's sluggish after 2500rpm and i can watch the coolant temp rise. As i stopped for a traffic light the coolant temp dropped drastically. I thought it might be the dirty cap and rotor i noticed while replacing the ICM so i got a new set. Idles a little better but still sluggish. I don't have a ton of money so i figured ask you guys first.

I'm thinking either the o2 or coolant temp sensor but there are no codes coming up.

Ideas?

You have air in your cooling system, but I don't see that causing the other problems. (Unless you are boiling some coolant and it is throwing off the temp sensor).

[This message has been edited by Gall757 (edited 04-14-2011).]

I don't think it's the coolant level as i get great heat and no bubbling sounds anywhere while hot. Went through that nightmare a few months ago. I will double check when i get it home tonight though. ya never know right?

Just strange that it heats up fast while accelerating then cools off just as fast when you stop.

Where's Phonedawgz?

I did notice on my drive home that the exhaust didn't seem as throaty so i'm starting to lean in the direction of a partially clogged cat... won't know till tomorrow if that is right or not.

I owned the car, sold it and recently got it back. When i had it the first time i removed the cat. The person who bought it from me put a used one on for some screwy reason.

For the last mile of my drive home she started to act right again then crap again after i slowed down a little. simply, weird.

That might be a problem, but how would it affect the coolant temp?

too much back pressure but the manifolds weren't glowing so i'm at a loss here.

Check your ground straps, and engine harness grounds. As engine moves around and gets warm, weird things happen.. cheap to check, and may explain strange sensor reading and spark hesitation / fuel injector misses..

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Currently in the middle of my 88 + 3800NA swap

Ill install my mega strap i built a few weeks ago, tomorrow.

Not a bad idea.

Check ECM connectors while engine is running. Give a wiggle and see if one is loose. Also check battery connections at C500. I had a stud terminal on the C500 come loose and give me very similar problems. Sounds like a power/ground issue to me.

Are you sure what the temp is actually doing. Since you where working on the dist. could you have bumped the temp sensor plug and wires? Is the plug on the sensor in bad shape? Can you verify with a scanner what the ecm thinks the temp is?
Although that would not explain the running changes since temp gauge has nothing to do with the engine operation.

exactly... my gauge is off to begin with but should have nothing to do with the sluggish driving.

An out of range coolant sensor can have similar problems without the ECM flagging the sensor as bad. I had a customer with a Ford F150 that ran horrible, didn't want to start after warmed up unless I applied full throttle and black smoke came out of the exhaust with a different exhaust note. I decided to ohm the coolant sensor and at 79F ambient temp had about 29 kilo ohms and the old one at the same ambient temp 8 mega ohms. Installed the new one and problem fixed. Check your timing also.

quote Originally posted by Finally_Mine_86_GT: too much back pressure but the manifolds weren't glowing so i'm at a loss here.

So are you saying the back pressure was reading high?

No... was explaining how a a partially clogged cat could cause the issue. My car i still have no idea.

A coolant sensor huh? anybody ever seen this happen with a fiero?

quote Originally posted by Dodgerunner: Are you sure what the temp is actually doing. Since you where working on the dist. could you have bumped the temp sensor plug and wires? Is the plug on the sensor in bad shape? Can you verify with a scanner what the ecm thinks the temp is? Although that would not explain the running changes since temp gauge has nothing to do with the engine operation.

Im gonna do this tonight. I have the aldl plug after all. (still trying to learn how to read the results)

[This message has been edited by Finally_Mine_86_GT (edited 04-15-2011).]

My best guess is the catalytic converter (if you have one) is clogged.

I'm thinking a restriction in the exhaust but it's going to be hard to tell with the on/off trouble.

If the temp is really dropping quite a bit at times that can pretty much only be caused by a stuck open thermostat. I doubt that is teh cause of the power problem.

I had a similar issue where the car died on me. I figured it was my alternator because my battery was also dead. Took to my new mechanic and he said it was my coolant temp sensor. He replaced the sensor and recommended a new battery so I went with that as well. Picked up the car at 3pm today and drove it around...so far so good.

The car should run with the coolant temperature sensor disconnected. It might be making the mixture way too lean - maybe. That said, I am not looking at your engine so yeah idk. Let's hope it takes care of everything for you.

Ok... didn't really get a chance to look it over on the weekend due to my wife having contractions and being at the hospital all weekend. (no baby yet) they subsided.

This morning i had to drive it to work (26miles) It ran great the first 2 miles, then started to act sluggish and the heat up and cool down problem didn't start till about 5 miles. When i get home tonight i'll be able to hook it up to the winaldl and find out more.

New symptom: never got the oil pressure gauge to work right. but before when i would come to a stop at a stop light it would bounce then hold around 50 till i took off again. Now it does the same thing and goes to about 5. Since the gauge sensor is no good i don't know if i should believe it.

Loose grounds, methinks.....

C500 is good. added new ground strap from engine to chassis. although motor is grounded directly to the battery. starting to think there might be something to the coolant temp sensor or possible dare i say, bad oil pump.

Did adding the ground strap change anything? How many miles on the motor?

Nope... didn't change anything. 151,000 not sure if ever when things were changed. Just never seen this problem before and can't afford trial and error with part changing. I've got about $50 to get this right or i need to look into getting something else on credit and be further in the hole.

I have a number of similar symptoms including a failed ICM which I suspect are related to a missing/disconnected ground. It's my understanding that the ICM ground wire goes to a ground connection on a bell housing bolt on the front driver's side of the engine. I haven't been able to find the ground wires anywhere in that area. I suspect this is one of many loose or missing items that resulted from a clutch replacement done by the previous owner. I've had good results from minor changes like grounds, battery connections, and vacuum hoses and connectors, which are likely rotted even if they look ok.

I've had a v6 icm fail before but never have one fail then deal with this. Literally went through 3/4 tank of gas in just shy of 50 miles. I did notice that when in 4th gear and stable on the peddle the car would buck a bit. Or if i was in gear and got off the peddle the car would bog down a lot faster then it used to.

Nobody knows what to look for with a winaldl log file?

bump back to page 1 cause i need to get this fixed in the worst way.

Update: I started to go through the wiring diagrams and everything else i could find on the subject. It looked as though the "Distributor reference pulse input" wire (purple/white) on the ICM might have had a bad connection. the connectors to the ICM looked their age so i used a very small screw driver and lightly pried the tabs up to make a better connection. It stumbled a little on start up and i wont be able to tell for sure till tomorrow. But i'll keep this updated cause as i see i'm not the only one with this problem.

Update #2: Drove it to work today and things seem better. Didn't gobble up a ton of gas and power seems to have been restored for the most part. The trip home will show it's true colors. Again... will post with updates.

Update #3: Drove home and tada fuel consumption problem mostly kicked. Not as sluggish as it was. Temp not going as high. might be on the right track here. I'll swap out the coil and give it some new plugs on friday when i get paid but right now it's a lot more tolerable.

[This message has been edited by Finally_Mine_86_GT (edited 04-20-2011).]

Ok... days later here it is.

Problem solved! Ty to those who tried to help.

ICM connections were bad. Also had one fouled plug. Plugs were new when the ICM decided to die but for some reason one plug fouled when the ICM crapped the bed or from running it so rich. The combination of the two resulted in hammering through 3/4 of a tank of gas in less then 60 miles.

The connector was bad? Or did you just have to re-bend something?

I just bent the tabs. I do at some point have to replace the connectors.