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Discussion Starter #1
Hello,
New to the forum.
I have a 92 ELDO with 96k miles.
Plugs, wire, cap--rotor--did not replace O2 sensors.
Tune up less than 8 months ago.
Replaced fuel filter, cleaned TB and EGR ports.
Checking fuel pressure regulator today.
Battery was disconnected---did a ISC/TPS "LEARN"
Engine stalls and/or surges even at highways speeds.
Noticed that speedo was all over the place also. Ranged from 0-80mph while cruising approx 55-60 mph.
Does the ISC or TPS output have anything to do with VSS input/output?
Need help.
Thanks
 

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'87 Coupe DeVille 4.1L FWD(New engine '08) 1981 F100 '03FXDL
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"Does the ISC or TPS output have anything to do with VSS input/output?"

The VSS: a generator geared to the output of the transmission, converts 'speed' to an electronic signal that 'tells' the ECM how fast the vehicle is traveling. An erratic speedo reading may be caused by the VSS being a tad loose in its fitting. There is a shim fix for that as I recall.

What codes are being shown? Why did you disconnect the battery? Why did you do that 'relearn'. Did you mess with either the TPS or ISC?. Has the speedo had erratic readings in the past?
Do you have the FSM for your car?
 

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Discussion Starter #3
"Does the ISC or TPS output have anything to do with VSS input/output?"

The VSS: a generator geared to the output of the transmission, converts 'speed' to an electronic signal that 'tells' the ECM how fast the vehicle is traveling. An erratic speedo reading may be caused by the VSS being a tad loose in its fitting. There is a shim fix for that as I recall.

What codes are being shown? Why did you disconnect the battery? Why did you do that 'relearn'. Did you mess with either the TPS or ISC?. Has the speedo had erratic readings in the past?
Do you have the FSM for your car?
Thanks Dave,

Yes, I have an FSM.
No, I haven't done anything with the TPS or ISC.
The speedo fluctuations started about 2 months ago.
Speed all over the place even though rpm is steady.
I thought a battery disconnect was a computer reset--similar to a "relearn"
I will check the connector on the VSS for a tight fit.
Current codes are:
E041---Cam position sensor????--might be intermittent--will check connector

History codes
E052--battery disconnected
I034--loss of PCM data
I039--Steering/suspension errors
I052---memory error
A050---Coolant temp too high???

When I turn the key on without starting the car:
---the EGR solenoid cycles for about 15-20 seconds
---the ISC ratchets about 20 times.

Thanks for the advice.
 

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'87 Coupe DeVille 4.1L FWD(New engine '08) 1981 F100 '03FXDL
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You have the FSM....a good thing.

Disconnecting power to the system results in erasing the RAM.....almost aways a bad thing. RAM is there to 'tweak' systems/sensors so the computer can manage the control systems according to its best ability. When the engine and its systems were out-of-the-box brand-new, everything ran off the default ROM values. The RAM then adjusts those ROM values as required. Erasing that RAM defaults everything to the ROM values and the RAM has to rebuild. The system can not adjust to optimum performance using the ROM values because everything is not new anymore. The 52 code and memory loss codes will always be set when the battery is disconnected. The RAM will rebuild with driving time....both highway/around town types.

I don't know if you can 'feel' a loose VSS. As I recall the shim needed was in the .005" thickness range. Now this problem may have been corrected by 1992, but it was a problem in earlier years.

When the Idle Speed control unit ratchets, the ECM is getting the wrong data it expects to be receiving. It's trying to adjust. Could be a faulty/misadjusted unit, a loose plunger, faulty/misadjusted TPS, loose wiring connections. There should be a 30 code set and maybe a 55. Go through the Switch tests to see what passes. Check parameters. Follow FSM procedures.
 

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Discussion Starter #5
Thanks again Dave,
I'll try all those things this evening.
When you say Switch test are you referring to the flow chart for diagnosing your symptoms????
I did check the ouput of the TPS earlier. The throttle angle seemed to increase smoothly as I increased pedal angle(after about 15-20 degrees of rotation).
There did seem to be a dead spot from about 5-15 degrees of pedal rotation. No matter how slowly and evenly I pushed the pedal the output jumped from 5deg to about 15deg. Is that the beginnings of a bad TPS.
 

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The switch tests I refer to are those in the ecm computer diagnostics accessible once the display reads .7.0. Also read about the Status Lights display on the ECC info center. There is a 'TPS test point' on the firewall where you can use a VOM to read voltage changes while you manupulate
the throttle by hand. The mechanical operation may need cleaning/lubing where it attaches to the throttle-plate. A TPS ain't cheap, so maybe it's only sticking and worth a close inspection. Check the throttle cable for smooth operation as well. It's always a detective story with these things......
 

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Discussion Starter #7
Hey Dave,
An observation today while working on the car. After about 5 minutes of warming up and running fine, the EGR solenoid started cycling on and off(about the same time the radiator fan came on). Shortly thereafter the car cut off. I manipulated the EGR valve by hand. It moved smoothly and was not sticking. The car had not really warmed up---the manifold was not hot to the touch yet---the EGR solenoid was "WARM". Does it normally get warm being associated with the EGR? Bad solenoid maybe. Is it telling the EGR to go crazy and stall the car out?
Will start with the ECM diagnostics you mentioned above.
Thanks.
 
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