1987 Chevy Suburban idles rough

REDWHITE

MEMBER
1987 CHEVROLET SUBURBAN
V8
4WD
AUTOMATIC
110,000 MILES

Noticed driving home from work, started to run rough no power. Next morning tried to test for problems. Idles up and down. Put in gear and tires to die then idles fast enough to move the truck then back down again. Pulled the vacuum hose from the MAP sensor and it idled much better. Bought a new MAP sensor and didn't help. Pulled the vacuum hose from the EGR sensor and no change. No codes on system need help. I did pull the vacuum hose from the air sensor and plugged into the egr valve and ran much better. This morning about 40 degrees outside rough idle, but engine had better response on acceleration. Afraid to take out on road.

2 Replies

JDL

MECHANIC
16,098 POSTS

If it only happens at idle, clean the idle air system. Does the injector spray pattern look ok? Fuel pressure good? How long since overall tune-up?

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Saturday, October 16th, 2010 AT 10:29 AM

REDWHITE

MEMBER
4 POSTS

I checked all vacuum lines, the gas flow at the trottle body looks good when engine is higher idle when it drops down like it going to die I notice the gas pattern look more like a mist. Then it picks back up again in idle and looks good. With the truck in gear and not brake the engine will advance enough to move the truck the bogges down for about 2-3 seconds and back up again.