This is the same ERRATIC ROUGH IDLE problem where I replace the EGR valve, IAC valve/solenoid, EVR solenoid with no improvement. This is on a 90 Bronco 351 w/ MAF conversion. No check engine light. MPG OK . Performance on freeway and hills OK. Has been running good (65k miles) until a bad alternator and battery was replaced. Alternator had a bad bridge diode and non-operating field coil relay. Tech said this could do harm to primary circuit components.

Rough idle is initially 1200 rpm at start then comes down about 200 rpm and oscillates up and down 100-200 rpm's.

Did a KOER code scan and got these codes which has me lost because they are
not failure codes of component:

15 ECA keep alive memory not working? open in the harness?
32 EVP sensor low voltage I checked the output w/ ohm meter and it varies as pintle moves. it also holds vacuum, no leaks.
38 ITS idle track switch open I don't think it has one, can't find it. Where is it located?
41 EGO signal voltage always low (lean) doesn't switch
53 TPS voltage too high
66 MAF sensor voltage signal too low

What do the above codes indicate?

What do you do with too high or too low voltage conditions?

Do I have a Bad ECU? Should I suspect Open or shorts in the MAF conversion harness?

Any help appreciated!

Ron

 

Here's what I've done about these two.

"32 EVP sensor low voltage I checked the output w/ ohm meter and it varies as pintle moves. it also holds vacuum, no leaks."

I checked my EVP sensor as well and it seemed to be working, but kept getting code. Replaced it and never got code again.


"53 TPS voltage too high"

TPS is on throttle body beneath the air intake(on a 1988 351 EFI)

TPS may be your problem. Some days the truck works fine and I have no surging or idle problems, but when it is having the most problems the TPS trips the computer. So there is obviously a problem with it and I will be replacing it.


Brian
1988 Eddie Bauer 351 EFI