87 Suburban running rough - The 1947 - Present Chevrolet & GMC Truck Message Board Network

cheepin · 07-12-2015, 11:49 PM

I have an 87 3/4ton Suburban. It is idling terrible. It will idle fine then jump up in rpms. If you blip the throttle it will idle fine again for a bit. Driving on the road it has a slight miss at part throttle at 35mph and lower. On interstate it is fine.
Now about a yr and half ago it was running terrible. So I did a good tune up. New plugs and wires. Helped but didn't fix. Had no codes. So I started changing sensors. Put a new (not rebuilt) distributer in. New o2 sensor,new coolant temp sensor, new IAC valve. Rebuilt the throttle body. No change finally found 2 of the new plugs were bad from the factory.
Back to current issue. It threw 2 codes. Map voltage high and o2 reading rich. Put new Map in ran better but not fixed. I don't know where to go now. Any suggestions?

Ski-me · 07-13-2015, 05:06 PM

EGR Valve?
Rebuild TBI unit? I think there is a diaphragm in there that can deteriorate (at least in my 89 there is).

cheepin · 07-13-2015, 10:27 PM

Quote:

Originally Posted by Ski-me

EGR Valve?
Rebuild TBI unit? I think there is a diaphragm in there that can deteriorate (at least in my 89 there is).

Yeah we did all new gaskets and such in the TBI unit. I'll check the egr valve.

cheepin · 07-26-2015, 03:46 PM

Well I haven't messed witht he egr yet. My kid decided to change the iac valve. This helped with the idle for a bit. Now it is is idling low and seems to be rich. Still think this could be the egr?

cheepin · 08-07-2015, 03:08 PM

So finally figured this out. It was the EGR sort of. When it started running rough I had found a broken plastic vacuum line. Well I got the EGR and Mapp lines reversed. Swapped back it runs great again. Jeez
Posted via Mobile Device

Ski-me · 08-09-2015, 09:34 AM

Great to hear, congrats!

07-12-2015, 11:49 PM	#1
cheepin Registered User Join Date: Nov 2009 Location: Parachute, CO Posts: 183	87 Suburban running rough I have an 87 3/4ton Suburban. It is idling terrible. It will idle fine then jump up in rpms. If you blip the throttle it will idle fine again for a bit. Driving on the road it has a slight miss at part throttle at 35mph and lower. On interstate it is fine. Now about a yr and half ago it was running terrible. So I did a good tune up. New plugs and wires. Helped but didn't fix. Had no codes. So I started changing sensors. Put a new (not rebuilt) distributer in. New o2 sensor,new coolant temp sensor, new IAC valve. Rebuilt the throttle body. No change finally found 2 of the new plugs were bad from the factory. Back to current issue. It threw 2 codes. Map voltage high and o2 reading rich. Put new Map in ran better but not fixed. I don't know where to go now. Any suggestions? __________________ 1984 1ton 4x4 crew cab dually 6.2 diesel,465,205,D60,D70,1987 3/4ton 4x4 suburban 5.7 FI350,TH400,208,1985 CJ-7 FI406,465,205,D60,FF14, 1970 Jeepster 350,465,205,D44,FF14,

07-13-2015, 05:06 PM	#2
Ski-me Registered User Join Date: May 2012 Location: Colo Springs, CO Posts: 870	Re: 87 Suburban running rough EGR Valve? Rebuild TBI unit? I think there is a diaphragm in there that can deteriorate (at least in my 89 there is). __________________ - Jeff 89' K5 Blazer, 2.5" lift, 35" tires 04' GMC Yukon XL, 3/4 ton, 8.1L

07-26-2015, 03:46 PM	#4
cheepin Registered User Join Date: Nov 2009 Location: Parachute, CO Posts: 183	Re: 87 Suburban running rough Well I haven't messed witht he egr yet. My kid decided to change the iac valve. This helped with the idle for a bit. Now it is is idling low and seems to be rich. Still think this could be the egr? __________________ 1984 1ton 4x4 crew cab dually 6.2 diesel,465,205,D60,D70,1987 3/4ton 4x4 suburban 5.7 FI350,TH400,208,1985 CJ-7 FI406,465,205,D60,FF14, 1970 Jeepster 350,465,205,D44,FF14,

08-07-2015, 03:08 PM	#5
cheepin Registered User Join Date: Nov 2009 Location: Parachute, CO Posts: 183	Re: 87 Suburban running rough So finally figured this out. It was the EGR sort of. When it started running rough I had found a broken plastic vacuum line. Well I got the EGR and Mapp lines reversed. Swapped back it runs great again. Jeez Posted via Mobile Device

08-09-2015, 09:34 AM	#6
Ski-me Registered User Join Date: May 2012 Location: Colo Springs, CO Posts: 870	Re: 87 Suburban running rough Great to hear, congrats! __________________ - Jeff 89' K5 Blazer, 2.5" lift, 35" tires 04' GMC Yukon XL, 3/4 ton, 8.1L



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