Idle Problem FINALLY located

[ltmark]

'85 L98- I have posted several threads asking for help for an idle problem. Have had many suggestions and spent many hours with my service manual. The problem was no fast idel at startup and "searching" idle until warm. Replaced most of the sensors and many other things that needed it or were best to do while I was at it. All IAC settings, TPS, injectors, etc. etc tested good or were replaced.

Finally I cut into the Coolant Temperature sensor wires and checked the voltages, according to the service manual. Suppose to read high (5 volts) voltage to the ECM when cold and low (1.5-2) when hot. I have 1.7 volts all the time, hot or cold. Bottom line is that the ECM got an engine hot signal from the sensor, which conflicted with all the other inputs when it was cold. Once it warmed up, it ran and idled well, with maybe a 10 rpm fluxuation at idle....I can live with that since you can see it in the dash readout but can't feel it!

Thanx for all the input. By the way, I fixed or was able to check several other non idle problems along the way, based on all the posts here on the site. A very Merry Christmas/Holiday to all you Vette folks!

 

[Moonunit 451]

WOW Great job! I'm having kinda the oposite problem and can't track it down. Mine will hunt and stall at startup and die if I don't even it out by just holding the R's steady at a thousand or so for about a minute. Then it's fine till I shut her down. When I start it back up warm and trow it in gear she'll try to die. I feather it up... and no trouble's till I shut it down again :confused

Been through replacing TPS and several resets of idle and voltage settings as recently as last Saturday, still doin' it and I like my idle a little lower than my pro buds keep setting it, so, I'm gonna bookmark this and look into it just as a possibility

She runs sweet otherwise, and this is an irritation I can certainly live with, but I'd like to track it down sometime.

 

[SSTibet]

Finally I cut into the Coolant Temperature sensor wires and checked the voltages, according to the service manual. Suppose to read high (5 volts) voltage to the ECM when cold and low (1.5-2) when hot. I have 1.7 volts all the time, hot or cold. Bottom line is that the ECM got an engine hot signal from the sensor, which conflicted with all the other inputs when it was cold. Once it warmed up, it ran and idled well, with maybe a 10 rpm fluxuation at idle....I can live with that since you can see it in the dash readout but can't feel it!

So, how did you fix the voltage problem? Did you replace the sensor?