Bad EGR?? Rough Idle

Reply Subscribe

Thread Tools

Search this Thread

Mar 21, 2026 | 12:59 AM

Jardin M. Bell

Thread Starter

Junior Member

Joined: Jun 2017

Posts: 28

Likes: 3

From: Baton Rouge, LA

Car: 92’ Camaro RS Convertible

Engine: 305 TBI

Bad EGR?? Rough Idle

My 305 is running rough at idle & acceleration.
Doesn't cut off, just runs rough.
I disconnected the bypass wire to set base timing, and it runs like normal.. once plugged back, runs rough again.
I did a smoke test for vacuum leaks and noticed smoke coming out of the EGR valve.
Is that normal? or is it leaking?
Can that cost the problem?

I’ve changed MAP sensor, IAC, TPS, & Spark Plugs.
Fuel pump & Filter are also new.

Mar 21, 2026 | 12:01 PM

Airwolfe

Supreme Member

iTrader: (9)

Joined: Oct 2020

Posts: 1,354

Likes: 634

From: Franklin, KY near Beech Bend Raceway, Corvette Plant and Museum.

Car: 1992 Pontiac Firebird

Engine: 5.0L L03 TBI

Transmission: 700R4

Axle/Gears: 2.73

Re: Bad EGR?? Rough Idle

Quote:

Originally Posted by Jardin M. Bell

My 305 is running rough at idle & acceleration. Doesn't cut off, just runs rough. I disconnected the bypass wire to set base timing, and it runs like normal.. once plugged back, runs rough again.

I did a smoke test for vacuum leaks and noticed smoke coming out of the EGR valve.

Is that normal? or is it leaking?

It's not normal. Either the EGR valve diaphragm is leaking or the EGR valve gasket is leaking.

Quote:

Originally Posted by Jardin M. Bell

Can that cause the problem?

Yes

Disconnect the vacuum hose going to the nipple on the EGR valve, lift up on the vacuum diaphragm, put your finger over the vacuum nipple on the EGR valve to seal it off and let go of the vacuum diaphragm. If it holds vacuum it's good. If it doesn't hold vacuum and the vacuum diaphragm goes back to its normal position then it is bad and will need to be replaced.

You can also test the EGR vacuum diaphragm with a MITYVAC Hand Vacuum Pump or something like it.