3400 engine gasping for air, reving out of control

[LZeppelin513]

I have a fiero with a 3400 installed running it with a 7730 ecm. The chip has a good tune by Ryan Hess. I have put about 300 miles on it so far with no problems other than i have a bad idle issue. i was also getting over 33 mpg. I was driving normal down the road when out of nowhere the engine started gasping for air (could hear loud sucking from air intake). Then the engine stumbled and revved way up to over 4500 rpms and then went to 5500 when i turned it off. Now it will only rev up to the highest when i turn on the car. I checked all the vitals like if any water lines fell off, all vacuum lines, oil, unpluged battery and plugged it back in and did a quick look to see if any electrical lines looked melted. everything that i looked at was normal so i am kinda stuck. any help would be spectacular. Thanks

Blake Tate

[bszopi]

Take out the IAC and see if it is stuck open.

[Superdave]

Take out the IAC and see if it is stuck open.

x2

then do an idle re-learn.

[PCGUY112887]

Can the IAC really open far enough to go to 5500rpm's?

[95Grand-Am]

Check your vacuum lines again. It sounds like a massive leak. You might want to check the one that goes to the break booster also.

[LZeppelin513]

Can the IAC really open far enough to go to 5500rpm's?

thats what i thought too.

i have had my engine run with a massive vac leak (ie. i forgot to connect the brake booster line up after i rebuilt the brake master cylinder) and it ran nothing like it is right now. I am going to go get some carb cleaner and spray around to see if i do have a vac leak tho but i have a strong feeling its something else.

Thanks a million for the help

[IanSzgatti]

do you have your 3400 ECM... plug it in and see if your problem goes away

[IsaacHayes]

Uh?? That OBDII 3400 ECM is not compatible with the OBDI wiring harnes...

[IanSzgatti]

Uh?? That OBDII 3400 ECM is not compatible with the OBDI wiring harnes...

good point

[Superdave]

Can the IAC really open far enough to go to 5500rpm's?

I've seen it get close to that...

[IanSzgatti]

I've seen it get close to that...

i have too... seen many a vac leaks bring cars to the limiter, but as for an all of a sudden scenerio, no i havent

[LZeppelin513]

Turns out it was just a vacuum leak after all. I was about to take off the iac today to see if it was the culprit when i noticed the port above the throttle body that goes to the top of the plenum was open. Stupid me must have looked over it when i was checking the engine out. But thanks for the replies, i am glad its back on the road.

Thanks
Blake

[2.8/3400 1985 Camaro]

Heh, when I first started reading this I was thinking vacuum leak all along and was just about to agree with the others that it was the probable culprit, but I guess you already discovered as much, glad you found it, lol.