Background:
Car is an 88 NA. S5 NA engine. No emissions. No 6 port. S5 manifolds with S4 TB. Car has run properly before.

Issue:
Car will barley run. Idle is non-existant. Must hold well over 3k for it to run at all. Even then, smells quite rich, pops a lot, etc.

Things I Have Done:
Checked all over for intake leaks
Swapped TPS
Swapped ECU
Swapped CAS
Swapped Fuel Pump
Run open AFM - verified AFM operation
Looked all over AGAIN for intake leaks
Verified spark
Verified fuel pressure
Pulled plugs - getting a slight bit fowled
Good compression


And now I am pretty stumped. Please assist me with any ideas or similar situations you have encountered and what resolved it.

Thanks,
-Jayson

 

Damn... GOTTA be a leak somewhere..

 

Change the coolant temp sensor. The one on the water neck on the engine. My car did the same exact thing. I changed it and that solved the problem. It will run rough right after you change it, it just needs to be cleared out.

 

Did you scan for codes? If the thermosensor went TU, it will pull a code.

 

Clean you bac valve ?

http://teamfc3s.org/info/articles/idle.html

 

Also check the electical connection plug on the BAC. My plug has came loose before.

 

Haven't checked codes yet, I think I am going to go to Rat Shack tomorrow and build me a tester once and for all.

Would the coolant temp sensor REALLY do something this serious?!!?

Thanks All,
-jayson

 

Very doubtful, the ECU defaults to 80c if there is a serious error with the sensor, there is basically (IIRC) no fuel adjustment at 80c so after a min or two of holding the throttle open (you can still be at low rpms though, like still at idle speed) the car will run fine.

So this is most likely not your issue, but if it is faulty, obviously change it.

 

Went out earlier and played with a few things. Made sure the temperature sensor was properly plugged in and all.

I don't have a BAC.

Anywho, I'm heading off to Rat Shack to get some LED's....

Bump for further ideas.

Thanks,
-Jayson

 

One other thing I should mention:
The ONLY way it will run is holding the throttle beyond %50. Even then, it seems to hunt through the rpm range some, when the throttle is held at one level.

Its bafffffffling.

 

Sounds to me, like, the most classic, vac. leak.

 

Pull both bottom plugs. Put your finger over one hole at a time and have someone crank the engine. Can you tell a difference in the pulses out the two holes? You might pull the EGI Comp fuse first.

Or....with someone holding the engine revs where it won't die....gingerly pull one of the LEAD coil wires up out of the COIL assy. Just up a tash. You should see the thing sparking. If not raise the wire out of the bore some more. Still no spark?

Either lead plug wire can go to either lower plug, but the trails must go where they are supposed to go. T1 to the fwd top plug and T2 to......

Some how check the timing. The rpms MUST be below 1000 rpm though. That might be a little difficult for you.

An air leak at one of the LARGE intake hoses......like that pipe that runs around the back of the dynamic champer and goes over to the left side where it ties into the air bypass solenoid (on a series four anyway).

 

Update:
I assembled a 2 LED code checker. I have tested it and the LED's light up fine. From the write-up that I read, I saw that both lights are supposed to come on for 2 seconds when you turn the ignition to ON. Mine does not do this. Would this be an indication of a big electrical problem???

please help

thanks
jayson

 

Yes, you have a big problem

 

BE sure both your primary injectors are firing. The 100% bulletproof way to do this is pull the manifolds, pull the injectors and rail back as a unit with wires connected, have someone crank the car over (use a rag to catch fuel shooting out) and see that both fire.

Are you SURE you have proper compression? Sounds like one rotor is not combusting, be it for lack of compression, fuel, or spark specific to that rotor.

A vacuum leak, if big enough, can act similar to this, but I'm going on your word that there are none.

Check compression. Check spark on each wire, and change plugs perhaps just to be sure one isn't fouling. Check both primary injectors for operation.