myf16

Should I expect to see a glowing catalyst if the coil is failing? I didn't see that. The car has only 150k miles and it has been kept mostly indoors in southern California.

Also, this car passed smog a year ago with as close to zero CO and HC as I've seen on any vehicle.

myf16

I changed the temp sensor. Contrary to the 1990 factory manual, mine was the 1-wire sensor with 12 mm hex, rather than the 2-wire 19 mm version shown in the manual. The car's misbehavior continues.

I wonder if my use of cooling system sealer a year ago caused this. It could have sealed a head gasket leak and left a lot of sealer in one of the cylinders, increasing the compression ratio and causing knocking when the engine is hot. But why would the engine care whether the transmission was in park or drive?

My next step will be either ignition coils or ECU rebuild (capacitors). Or I may just live with the problem.

myf16

The CO section of my 1990 factory manual shows a 2-terminal coolant temp switch on the driver's side of the radiator. My July 1990 manufactured 1990 model has nothing electrical in that area or anywhere else I can see on the radiator. I'm thinking that switch is absent from my car.

According to the book, that switch controls the two electric fans on the A/C condenser. They don't appear to be needed to keep the operating temperature down. I don't use the A/C since the compressor seized and I disconnected its electric clutch.

I have no idea where the water temp switch could be hidden if I have one.

myf16

My current plan for a few weeks from now is to warm the car up until the problem appears, then using a can of freeze spray on each ignition coil then on the ECU. If the problem persists despite cooling these components, I will look elsewhere or give up.

myf16

Switching off overdrive helped a lot, which is consistent with this hypothesis. So I'm going to use Sea Foam next if I can figure out where I can do so without creating a fuss. With luck this will burn any sealant crud out of the cylinder.

Jeik

Please keep posting, I am having the exact same problem where it drives fine from a cold start but as soon as it is warmed up, it loses power and when in drive, won't rev past 2000. I tried replacing the ecu that I got from ebay, really crappy looking ecu but I figured what was the chance that two ecu's had the same capacitors wrong. I checked the codes on the obd1 (I have a 92) using the paper clip trick and counting the number of check engine light blinks. I got three codes, 25, 41, 55 which is air-fuel ratio is running lean, throttle position sensor malfunction, and no2 knock sensor. So I think, from what I have read, that because I am running lean, the car won't run right but I don't know how to diagnose the problem of running lean...plugs, wires, vacuum leak, egr problem. I just ordered a tps from amazon, about 22 bucks, hopefully it fixes something but I'll let you know if the tps change helps. No one has let me know how to fix my codes yet so I am playing the guessing game now. I also got some new spark plugs I'm going to try and install this weekend if I have time.

myf16

I ran 2/3 of a bottle of Sea Foam ($8 at Target) through the engine 2 days ago. The missing or misfiring or mild bucking or whatever it was is happening much less often. I drove 20 minutes from a cold start with no symptoms at all. I decided to run the rest of the bottle through tonight. I will let you know how it works out.

My technique was: Detach the 8 inch fat hose at the front of the engine, the one that feeds the idle air valve, at the MAF end. Hang a loooong funnel (from Harbor Freight) from the front edge of the raised hood. Insert the funnel into the hose end. Remove the cover over the throttle linkage (two 10 mm bolts plus one nut). Start the engine. Run over to the throttle linkage and keep the rpms up. Pour fluid slowly into the funnel. Stall or turn off the engine quickly after pouring the desired amount of fluid. Try not to gag from the exhaust fumes. Wait 20 to 30 minutes. Drive it hard for 5 minutes or so near neighbors you don't like or near fields needing to be fumigated. Done.

I'm starting to believe my hypothesis about deposits or some sort in one cylinder. I wonder what other deposit removal methods are available if this doesn't solve it.

Yamae

Does your ECU have Marcon electrolytic capacitors inside like other early productions?

myf16

I have never removed the ECU. Manufacture date is 07/90. It's a southern California car mostly garaged and used at least weekly, so the caps are getting exercise and not a whole lot of heat or cold.

Jeik

I was throwing a tps malfunction code so I replaced the tps. I also replaced the air filter, did not change anything. I know this isn't much help but just adding to the list of things done that have failed so you don't have to try it yourself. I personally think that the reason I'm having this problem is because I am running lean. I got an error code saying that my air to fuel ratio is running lean and I think this has something to do with it. I am going to try and clean out my egr valve to see if it helps. My car smells not great when idling and driving and from what I have read, running lean and having a bad egr valve contributes to the bad smell so I am going to see.

myf16

I love this car! It's running perfectly now as nearly as I can tell. Who would have thought that an $8 can of Sea Foam could actually solve a problem?

Jeik

Wow, that's crazy. Well, since you said it worked, I am gonna give it a go. It shifts smooth in Drive now and will rev past 2k at full throttle now?

myf16

My problem was different. It was misfiring occasionally when hot but it never failed to respond to throttle and it always shifted correctly. I believe that one cylinder had some excess leak sealer reducing its volume and increasing compression, and that the Sea Foam burned out that excess sealer.

Jeik

I see, thanks anyway for the info

myf16

There is sometimes a subtle misfire, but it's much much less than before, barely noticeable. In case one cylinder still has material in it I will wait a year or so for the Bars Leaks sealer material to burn out then I will retreat with Sea Foam. I asked the Bars Leaks people to consider running a test with Sea Foam to find out whether they can work well together.