I just swapped in a b16 into my 94 coupe, everything runs great and drives great except after abought 20 min of driving the engine will sometimes vary the idle speed with a difference of 200-300 rpm(for example it will rev up then down and repeat) . The check engine light will come on and give me a code of 23 which is the knock sensor. I checked out the service manual and it did not look like the knock sensor should have anything to do with the idle problem. I also checked the iacv, fast idle and associated plugs and wires and everything appears to be good. Any ideas on what it could be?thanks

 

did you check your TPS.. that could be the problem, was the b16 bored or anything if it is .. you probably need higher cc injectors, but if not just check the tps! a buddy of mine had a similar problem GL!

 

I suggest cleaning both IACV and fast idle valve with brake cleaner, replace the knock sensor since the ECU indicates its bad. Check for your vacuum leaks as well. Any other CEL codes?

 

What year b16? JDM or US? If you have a jumper harness, you should check that out. I had a problem with mine, a wire came off and it was throwing a code 3 (map sensor). If everything is straight with the wiring, it might be your tps...

 

The engine is a b16a3 out of a del sol, it is not bored or anything like that. And I am not getting any other codes. I am guessing that the tps, a dirty iacv, or a dirty fast idle would not give a code?