MAP sensor question

[88 Beast]

Been battling the intermittent high idle at start up (hot or cold engine)for what seems forever. IAC motor, CPS and 02 sensor are new. Ohmed out MAT and CTS sensors today per Chrysler Renix FI System t/s and repair specs.( found link here somewhere, lots of good info)and checked out good. Tested MAP sensor, input volts @ 5, specs 4.5-5. Output volts 3.67, spec says 4.5-5 and replace if not in spec. Started truck and was operating within spec of.05-1.8 volts at idle. My question is if the altitude of 6200 ft. here would make a difference in the output voltage of the Maps. I'm getting alitte tired of throwing parts at this but want it fixed as it's my DD. Any input would be great. BTW, I've checked all the normal stuff; vacuum leaks, grounds,etc. Thanks

[Geonovast]

Do you have the high altitude CPS?

[88 Beast]

Yup.

[HOrnbrod]

I don't think it's the MAP sensor. Sounds like a vacuum leak - suggest trying these two checks.

 

1. Disconnect the brake booster vac line, plug it, then try.

2. Disconnect the EGR vac line and see if that makes a change in idle RPM.

[carnuck]

Take the MAP hose and spray it out with TBI cleaner. Then check for vacuum leaks. Then take apart the C101 connector (above the brake booster on all 87/88 and some '89s with 4.0L) and electronic contact cleaner

[TrailReadyMJ]

Check your TPS sensor. This is the most common cause of high idle at start up. Probably just needs adjusting. I just went through the same thing.

 

If it was a vacuum leak, it's doubtful to be an intermittent issue. If the MAP is bad, your more likely to have a low/rough idle. These would also cause problems the whole time, not just at start up.

[88 Beast]

Thanks all for the input. I'll do some more t/sing and try and get this figured out.