My 85 Iroc I just did a 305-350 TPI swap has an erratic idle and is very hesitant when giving it gas. I have changed the injectors to 22lbs, switched proms and limp mode chips from a 85 corvette 350 TPI (the reason I chose a corvette for the chips is GM only made one 350 TPI in 85, which was the corvette, And the ecm's matched) I changed the esc and knock sensors. When I start it up the idle will shoot to about 1200 and drop idle to around 500, then stall (sometimes this happens a few times) Then the next time I crank it over it may shoot to 1000 maybe but stay idling around 700-400 rpms and start bouncing all over from 1000 to 300, almost stalling, kick back up... over and over again... Plus when I give it gas, the response is horrible. Sometimes the rpms may drop almost to stall or rise a few seconds after pressing the gas. I don’t understand whats going on with it. Some days it loves to run and I can make her scream like a raped pig and others it does like me. Anyone have any ideas? Thanks..

Check your fuel pressure and make sure it is not fluctuating.

I checked the fuel pressure, its not flucutating at all. Stays constant when running. I have a ERG failure on the check engine, I dont think that would cause my idling problem and hesitation, do you?

A dirty EGR valve, stuck open will act like a vacuum leak.

Stuck shut will not be noticeable, only set code after about 10 mins of driving.

Unplug the IAC after turning key on, engine off and see what kind of idle symptom you get. Do this after the first warm up. Idle should be high and steady.

Thanks for the input, I unplugged the IAC and it did idle high and steady for awhile then dropped down to about 500rpm with improved reaction when pressing the gas. Would that mean a bad IAC sensor?

I have pulled the EGR valve and it’s not stuck. I cleaned and put it back as well as tested the solenoid which came out ok. I think I might buy a vacuum tester and test all the lines.

If the IAC was retracted, the Idle would be high, it was. I am not sure why the idle came down to 500, It should have stayed at the high idle speed as long as the IAC was retracted.

All this means is, that it would unlikely be the IAC, unless the passage way is pluged up. Something lowered the amount of air to the engine to drop the RPM or the fuel got way rich. Check the plugs at idle and smell exhaust for richness.

i forgot to plug one of the vaccum hoses in off the egr solenoid and my car idled like that.

Hey I'm having kind of the same problem and I was wondering if some1 could help. I have the 305 with a throttle body. When I start it up the RPM's jump around and then the car stalls just like his. I thought at first it was just a vacuum leak because I had a hole in a hose that made a loud hissing sound. But when I replaced that hose it ran just fine 4 about 2 weeks an then it started stalling and idleing funny. So I think I might have another air leak but I don't know where it would b. Also when I'm driving, and I give it gas sometimes it will take the car a second to realize that I'm pusshing the pedal down. I've also noticed that when I am just coasting and do not have my foot on the pedal I sometimes feel the car acelerating like my foot is on the gas. But it usually stops when I hit the brakes. The other day I started it up 4 the first time in 3 days an of course it was acting funny so I took it around the block to see if it just needed to b drivin alittle and at first it was doing fine but then everything started acting up again only this time when it gave it's self gas and I hit the brakes it continued to give it's self gas. I have no clue what I'm doing but I have a friend that works on cars thats been trying to help me but he has an RX7 with a rotary engine so he's not the best when it comes to my engine. I really love my car and if any1 could give me some advice on what they think the problem is I would b very grateful.