The car is an 87 trans am 305 tpi auto. I am getting a code 42 after the engine temp reaches 190 roughly.

When the code sets the engine feels sluggish/lacking power, backfire in muffler after letting off the gas. Also the temp runs 20 degrees higher than normal, the idle feels okay. Taking off from a stop the engine feels bogged down until i get to 10? mph then feels like it has more power.

I went through the service manual flow chart for code 42. I got 556 ohms on curcuit 423?(don't remember exactly, but the white wire coming from icm) the manual says no more than 500. The white wire(ohmed out good) and connections look good. Replaced icm with a new one that tested good 3 times in a row and the car wouldn't even start with that one.

Any input on my next step would be greatly appreciated

 

also had the tach go wild when crusing at 2000 rpm, it would jump from 1000 to 4000. It stopped after a couple of miles.

 

checked cts and tps both are good, fuel pressure is good

 

make sure the tac lead is not grounding on the coil

 

will check into thanks!

 

any results yet? im battling a code 42 also

 

make sure ur EST is connected,reset ecm by disconnecting neg battery cable for a couple min.

 

Did this ever get fixed? Im having a stupid code 42 and looking for some things to check

 

late response

close, purple wire going to coil got pinched and caused an open, thanks for the help was tricky to find

 

Does anyone have the service manual flow chart for Code 42 that they can post? Im having the same problem and throwing this code.... would be helpful!

Thank you!

 

Bump on this question...

 

http://chevythunder.com/est_code_42.htm

 

Thanks!