Tough idle problem

[j911brick]

Who likes a challenge? I have a 97 993 motor installed in an earlier (75 to be exact) car. Car starts right up, but after a few few seconds settles into a very, very low idle. Blocking half the intake improves the idle significantly. Checked for air leaks with starter fluid and with smoker. New MAF and plug wires. Only CEL code present are related to the varioram flappers.

Any guesses?

[bbturbo]

I would see if the idle stabilizing valve is dirty and clean the intake through throttle body. I removed mine and cleaned it out recently. Take some brake cleaner and spray the ISV out well, then make sure you put it on the correct way. If it's on backwards, the car can have serious idle issues. Someone put mine on backwards during another service and it was a mess trying to figure it out.

This may not help, but at least it will be clean and sensing air better.

[TMc993]

Originally Posted by bbturbo

I would see if the idle stabilizing valve is dirty....

+1 - DIY here: Idle Stabilizer Valve Cleanout DIY

[j911brick]

Thanks for the replies. I cleaned the ISV with no change. I then moved on to the distributor caps and rotors. When got to the secondary rotor I noticed it spin freely. Obviously a broken belt. But it doesnt end there... I put another distributor in and the car ran the same. I checked the coils and the secondary was not not firing. But wait, theres more...Changed coils and it still did not work. I traced back the wiring and found there is no wire for the secondary coil in the chassis harness. I am now trying to sort that out.

[j911brick]

In case anybody is still paying attention. I finally concluded that this not the correct wiring harness for this motor. So I finally completed the arduous task of moving around a couple of the wires and got the secondary coil firing. But still, the car really didnt run any better. Since I knew the wiring harness was wrong, and a couple wires were allready misplaced, I decided to investigate the rest of the harness. I started with the MAF and concluded that one of the wires had too much resistance. Then I found this:


Now the car idles and runs good.

[wesleyc]

Congratulations on good trouble shooting !

[j911brick]

Originally Posted by wesleyc

Congratulations on good trouble shooting !

Quite a few hours and definitely not a typical type of situation.

[j911brick]

WHy would somebody do this?

Originally Posted by j911brick

Now the car idles and runs good.

[wesleyc]

Originally Posted by j911brick

WHy would somebody do this?

You got me ? I bought a 993 in the Houston area and the shifting mechanism was so wore out you could almost not get it in reverse. Drove it back to Oklahoma. Put a shift kit in it and shifted great. Why not spend the $ to get more $ ? My point is people do stupid stuff.

[TMc993]

Originally Posted by j911brick

Why would somebody do this?

I suspect the answer to you question lies in this sentence:

Originally Posted by j911brick

I have a 97 993 motor installed in an earlier (75 to be exact) car.

Someone probably got to the end of their patience or budget, or both, and just cobbled it together.

[j911brick]

Originally Posted by TMc993

Someone probably got to the end of their patience or budget, or both, and just cobbled it together.

I actually bought the motor from LA Dismantlers and did the conversion into the 75 myself. I think the harness came from a third car.

[TMc993]

Originally Posted by j911brick

I actually bought the motor from LA Dismantlers and did the conversion into the 75 myself. I think the harness came from a third car.

No disrespect intended. I interpreted your previous posts to be saying that you had acquired the car intact and had discovered that it had the incorrect wiring harness after the fact.

[Nine9six]

Originally Posted by TMc993

No disrespect intended. I interpreted your previous posts to be saying that you had acquired the car intact and had discovered that it had the incorrect wiring harness after the fact.

I thought the same thing as Terry, but it doesn't much matter since the problem has been resolved.

[bbturbo]

Nice work!

[j911brick]

Originally Posted by TMc993

No disrespect intended. I interpreted your previous posts to be saying that you had acquired the car intact and had discovered that it had the incorrect wiring harness after the fact.

Sorry if you found that misleading. I thought I was using the appropriate amount of pertinent info.