How many miles on the engine??? Since it's an IROC, I'm going to assume TPI. I'd pull the connectors off the injectors (one at a time) and measure the resistance with an ohm meter. Anywhere from 14.0 or greater ohms would be acceptable. Anything below that would more than likely need replaced. But keep in mind that an ohms test isn't the only way to diagnose a bad injector. An injector can have a good ohms reading, yet have a bad spray pattern or balance. The only way to test these two parameters would be to send them in and have them tested.
Have you also checked fuel pressure? This can also cause what feels like a misfire. Low fuel pressure can be from a clogged filter to a weak pump.
You can also test the MAF sensor by tapping lightly on it with a screwdriver while the engine is running. Any change in the runnability while performing this may be cause for a bad MAF sensor.
Just remember, these are all "backyard" tests but can hopefully lead you in the right direction.
<BLOCKQUOTE>quote:</font><HR>Originally posted by davidpozzi: under what throttle conditions does it miss?
Part throttle or full.
What about after 2000, it runs fine?
any other details?
Problem is only between idle and 2000rpm.
Thanks to all for your suggestions.
We are trying these out.