Let me first say that I did ton of research and google about Honda notorious idle control issue. But I am completely lost here and do not know where else to check. I have ruled out many of the possibilities that may link to the idle issue. But I suspect that it may more to it than that. I have a 1991 Honda CRX HF (D15B6). I recently replaced the D15B6 engine that was originally in the car with a fully rebuilt D15B6 engine due to a spun bearing. After the installation of the engine, I test drove it for 10 miles and noticed that it started to have idle issues. The idle would be running normal but once in a while it would drop from 1000 to 500. I also tried revving the engine to a higher rpm and maintaining it at a constant 2000 rpm. However, the rpm would drop from 2000 to 1500. It feels as if I turned off the engine and quickly turning it back on. Everytime the RPM drops, the CEL would come on momentarily and it goes away. I checked the ECU for flashing red lights but there are none.

I checked the voltage on the TPS and found that it was 0.5 volts closed but at WOT it would not go higher than 2.6 volts. I tried it with 3-4 other TPS sensors and I could not get it to be at the ideal 5 volts. I did not check the IACV as many had suggested. I checked the grounds but everything is hooked up properly. I checked for vac leaks but everything seems to be good working order. But I suspect that it may be due to a bad ground somewhere that I did not check. I checked for ignition timing as well. Additionally, I did notice that the radiator fan does not kick on after reaching the correct temperature. Any help would be greatly appreciated. Thanks!

 

Anyone?