I have nearly completed a D16ZC SOHC (Vtec) swap into my 90 CRX HF (With Si tranny- Quaife LSD). Everything is working great. No CEL's, and the engine starts up easily and idles smoothly when cold.

Once warmed up, the idle drops to a rock solid 650 RPM. As a matter of fact, it is probably the most solid idling engine I have ever worked on!

Under load, the engine maintains RPM very steadily, and it has very good power (Well, as good as a D series can have.. LOL)

But I have this nasty off-idle stumble that is driving me nuts!

When I did the swap, I maintained the "Peak and hold" injectors from the D15 that was in the car, complete with resistor box. But I cleaned the injectors very well and I know they are working properly. Plus, under load, the car has no stumble at all, even when hammering it from say 1500 RPM.

I am using a virgin P-28 that came out of a 95 Civic (Auto, converted to manual).

I am at a total loss right now with this stumbling problem. It makes it very difficult to drive in heavy, bumper to bumper traffic.

If this were a naturally aspirated engine, I would swear that I had a power valve problem, and if it had a Holley carb on it, I would have the thing purring like a kitten in about 30 minutes...

So, if anyone has any thoughts on this, I would appreciate you sharing your ideas...

BTW: Timing is set at +16 degrees.

 

so your saying that its not naturally aspirated? that means u got a turbo or supercharger(forced induction)

 

Sorry for the confusion... It is not carburated... I was thinking of one thing and typing another.

I have searched this topic extensively, and others have reached the conclusion that they had a semi-faulty TPS. I just read elsewhere that a TPS can have a dead spot in the sensor and still not give a code. If this is true, then I would have to say the engine responds exactly the way a faulty TPS would react. At first I thought it was a vacuum leak, but the idle is way too steady for that. Plus I couldnt find a leak anywhere, anyways.

Could a failing cat give an off-idle stumble? I havent run new exhaust yet, but did detect the "Rotten egg" smell when the car warmed up. Just thinking out loud...

 

measure the tps voltages. or unplug it and see what happens?