Odd cold idle issue 84
Thread Starter
Race Car
Joined: Dec 2006
Posts: 4,089
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From: Tampa Florida
Odd cold idle issue 84
84 5-speed
Been working on an 84 that was just purchased and had all type of strange issues. Idle would change from 600-1100 Rpms with no apparent constancy. When headlamps are operated the car would stall due to large voltage drop. The alternator would go to about 10volts and Christmas tree the dash. After a lot of hunting the 30 bus feeding the Fp, Ox sensor, Temp sensor and Icv was replaced with a 25Amp fuse it calls for a 16Amp. Every connector on the wiring harness had been molested and it was routed under the harmonic balancer. What I found is the Icv and Temp sensor connectors were reversed and the Idle control switch was loose and not functioning. I have replaced the Temp sensor and corrected the Idle switch adjusted the idle and timing. For once the car started immediately Idle was stable headlamps now work without shutting the car off.
Since all the testing was done warm I thought This was the end of the problems. What is happening when sitting overnight and cold it’s starts as expected but the idle sits at 400 Rpms and idles rock solid, if the headlamps are turned on it stalls due to a larger voltage drop. The last repair involved the Idle switch adjustment before it started acting up. As it warms up Idle gets higher and sits in the high 700’s and runs great.
Since I found all the wiring issues more then I mentioned I can assume the P.O. got into the Afm and may have played with that. What is not making sense is at 400 Rpms why It idles so smooth. Any feedback would be appreciated.
Been working on an 84 that was just purchased and had all type of strange issues. Idle would change from 600-1100 Rpms with no apparent constancy. When headlamps are operated the car would stall due to large voltage drop. The alternator would go to about 10volts and Christmas tree the dash. After a lot of hunting the 30 bus feeding the Fp, Ox sensor, Temp sensor and Icv was replaced with a 25Amp fuse it calls for a 16Amp. Every connector on the wiring harness had been molested and it was routed under the harmonic balancer. What I found is the Icv and Temp sensor connectors were reversed and the Idle control switch was loose and not functioning. I have replaced the Temp sensor and corrected the Idle switch adjusted the idle and timing. For once the car started immediately Idle was stable headlamps now work without shutting the car off.
Since all the testing was done warm I thought This was the end of the problems. What is happening when sitting overnight and cold it’s starts as expected but the idle sits at 400 Rpms and idles rock solid, if the headlamps are turned on it stalls due to a larger voltage drop. The last repair involved the Idle switch adjustment before it started acting up. As it warms up Idle gets higher and sits in the high 700’s and runs great.
Since I found all the wiring issues more then I mentioned I can assume the P.O. got into the Afm and may have played with that. What is not making sense is at 400 Rpms why It idles so smooth. Any feedback would be appreciated.
Nordschleife Master
Joined: May 2012
Posts: 5,216
Likes: 431
From: Thousand Oaks California
As usual, replace the Temp II sensor if it is original as it can cause all kinds of running issues. It may be out of spec when cold and within spec when hot.
They're cheap and a consumable part that should be preemptively replaced every 6 years or when you do a timing belt change.
They're cheap and a consumable part that should be preemptively replaced every 6 years or when you do a timing belt change.
Rennlist Member
Joined: Mar 2002
Posts: 6,114
Likes: 344
From: Texas
Thanks for that. I saw the term "AFM" and thought that it was probably a US version, but sometimes people use terms like that interchangeably with "MAF" and vice versa, so I just wanted to clarify.
I know you posted that you replaced the temp sensor, was it the temp II?
I know you posted that you replaced the temp sensor, was it the temp II?
Thread Starter
Race Car
Joined: Dec 2006
Posts: 4,089
Likes: 6
From: Tampa Florida
It’s the Temp sensor but the 84 has only one sensor not two like the Lh models. Yes it was replaced the only thing that comes to mind is the Po opened up the Afm and may have played with it. I believe her went on a mission to get the car running after unknowingly swapped the Temp sensor and Acv. The car is rock steady at 400 Rpms when cold never seen that before. During testing I did not have this issue until I corrected the idle switch that was not working.
I ordered the Temp sensor from Fcp Euro beginning to think that might have something to do with it.
Bosch 0280130026
I ordered the Temp sensor from Fcp Euro beginning to think that might have something to do with it.
Bosch 0280130026
Porsche 928
- 1980 Porsche 928 Engine Temperature Sensor
- 1980 Porsche 928 Base 4.5L V8 Engine Temperature Sensor
- 1981 Porsche 928 Engine Temperature Sensor
- 1981 Porsche 928 Base 4.5L V8 Engine Temperature Sensor
- 1982 Porsche 928 Engine Temperature Sensor
- 1982 Porsche 928 Base 4.5L V8 Engine Temperature Sensor
- 1983 Porsche 928 Engine Temperature Sensor
- 1983 Porsche 928 S 4.7L V8 Engine Temperature Sensor
- 1984 Porsche 928 Engine Temperature Sensor
- 1984 Porsche 928 S 4.7L V8 Engine Temperature Sensor
Rennlist Member
Joined: Mar 2002
Posts: 6,114
Likes: 344
From: Texas
Tampa,
Porsche Classic parts shows 2 temp sensors. 928-606-125-01 is the temp II and 908-606-201-01 is the coolant temp sensor. Look at illustration 902-06 Items I and L
I'm not saying this is your problem, but it could be.
Porsche Classic parts shows 2 temp sensors. 928-606-125-01 is the temp II and 908-606-201-01 is the coolant temp sensor. Look at illustration 902-06 Items I and L
I'm not saying this is your problem, but it could be.
Last edited by soontobered84; Jan 25, 2018 at 07:23 PM. Reason: add part numbers
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Thread Starter
Race Car
Joined: Dec 2006
Posts: 4,089
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From: Tampa Florida
It turned out 1 turn of the Tb screw did it when cold out to about 3.5 turns I believe the air stabilization keep it running and not stalling.car is 50miles south of me so owner tried it and now things are in line. Now a reported surging under load needs to be looked at.