I drive a 1985 Fiero with a 4.9L conversion from the Fiero Factory. The following upgrades were added shortly after the install of the 4.9L:
• Vss signal connected to the Caddy ECM.
• Also had my MEM-CAL Chip reprogrammed by Fiero Addiction.

Fast forward several years and I had to have the injectors replaced, but another problem appeared and may be a coincidence.

The engine starts on fast idle (2000 Rpm) and drives normally with no stalling, but idles at 1200-1500 RPM. I have twice replaced the ISC motor following the adjustment procedure, replaced the ECM, checked and reset the TPS setting, checked for obvious vacuum leaks, cleaned the throttle plate, and ran several code scans, with no improvement whatsoever.

If you have any ideas or recommendations I would really appreciate your response

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JT328

Are you sure it's really idling at 1200+?

Mine is a Fiero Factory conversion. They did nothing with the tach to accommodate the additional cylinders.
My actual RPMs are 3/4 of what the tach reads.

Raydar,

It never occurred to me that the tach in the car is reading incorrectly. I will check with an external tach, however it seems fast when you listen to the engine. Did you ever resolve the issue of the wrong tach reading?

Thanks

Forum member JGunsett does a superb job on tach recalibrations.

quote Originally posted by JohnT328: Raydar, It never occurred to me that the tach in the car is reading incorrectly. I will check with an external tach, however it seems fast when you listen to the engine. Did you ever resolve the issue of the wrong tach reading? Thanks

It *sounds* like it's correct. It really does. Except at idle and "redline".
Mine idles at ~1200 (indicated) and likes to shift at ~5500 (indicated). A 4.9 does neither.
A scan tool shows that the tach is reading 4/3 of actual RPM.

Having said all that, I found that my 4.9 idled too low to suit me (I have a manual tranny.)
I bumped my idle speed up to ~900 RPM. Stock is around 750.
It also fixed the "low oil pressure" light.

quote Originally posted by olejoedad: Forum member JGunsett does a superb job on tach recalibrations.