4.3 Bad Idle

[Boyd Dawson]

I have a 1986 Astro with a 4.3 At idle it runs rough. Just above idle it runs fine. I have had two Astro and a friend had one that all run the same. All 86-89 models. I have changed plugs, wire, rebuilt throttle body, replaced Egr (GM). The engine has 200k but out side of the idle the engine run fine. I saw a post from another guy that changed the egr and it was fine. I have heard of doing a smoke test on the engine to look for leaks. Thanks for your help.

[hotrodtech.]

most 4.3 engines have a rough idle idle due to the balance of the engine, there is really no way to repair this problem

[RABarrett]

It is first necessary to determine whether the miss is ignition or fuel related. My Safari is an '85 with 250,000 miles on it. It idles perfectly @500 in drive. Walk back to the exhaust pipe and listen, or place your hand into the exhaust stream, well away from the pipe outlet. If a miss is heard or felt, that is a clue as to the cause. Intermittent misses are typically fuel related, but may also be caused by the ignition. Fuel related misses also involve the EGR system as they dilute the mixture. Steady misses are easier to find. Typically removing a plug wire from the cap will either make the problem worse, or have no effect. When plug wire removal has no effect, you have found the cylinder with the problem. Go from there to plugs, wires, compression testing, etc. Ray

[Bdav123]

It could also be the oxygen sensor my 89 safari did the same thing until I got it fixed. Oh and one more thing the 4.3L engines run fine I have one in my 99 Astro