I have an 86 IROC LG4 with the stock Quadrajet that was rebuilt 3 or 4 months ago. My problem is that the car shakes badly at idle kind of like a miss and feels like it wants to stall. It used to surge and buck under acceleration but that has seemed to go away. The car used to do this every once in a while, but would go away after 20 minutes or if I turned off the car and restarted it. I have taken it to two dealers a total of 5 or 6 times and they can't figure anything out. I have replaced; O2 sensor, plugs, wires, cap, rotor, coil, ignition module, egr valve & solenoid, CTS, fuel filter, and a week ago the ECM. I also checked the pickup coil and the resistance was right at 800 ohms. The car also seems to be running a lot hotter, like sitting still the temp rises a lot faster than it used to. When I replaced the plugs they weren't very old but were pretty carbon fouled. Also I hooked up my scanner and saw that at idle the egr duty cycle was 49.9%. It also stalls sometimes when its cold soon after the choke comes off, which it has never done before. The idle gets too low and without revving it it just dies. Before if the idle got too low something (I thought the computer) would always bump it up a few hundred rpms and it would smooth right out, but that just doesn't happen anymore and I think that is a big part of the problem. I don't know what to do anymore and am ready to give up. I appreciate any help you can give me (sorry its so long).

Thank You

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86 IROC-Z
Stock LG4
700R4

[This message has been edited by Red86IROC (edited October 31, 2000).]

 

I know you've taken it to the dealers, but by any chance did you check the timing? I had a problem with my old 84 LG4 that was similar and my timing was off.
Randy

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Randy
84 Trans AM LG4, 700R4 T-tops
1984 Z28 L69, 5 Spd, T-tops
"Don't sweat the petty things...Just pet the sweaty things"

 

or maybe a vacuum leak....i dont see how 5 or 6 places could miss a vac leak but i would check for one...and replace any hoses that look close to ****ty

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350, Comp 262, Edelbrock Performer intake 600 cfm carb and exhaust, headers

 

Sounds to me like the plugs in the base of the fuel bowl (the 8 little ones under the primaries, not the 2 big ones under the secondary rods), where they are exposed to vacuum, have leaks. Old Q-jets almost always do that.

Take the throttle body off; wire-brush and sand to clean metal all around the plugs, wash them with lacquer thinner or other totally-evaporating solvent, and coat them thoroughly with epoxy. Let it set up completely before filling the carb back up with gas.

I can't believe people will take customers' money to rebuild one of those, and not do that; but I don't think I have ever seen a shop (dealer or otherwise) actually fix that one thing that is nearly always the most serious problem with that kind of carb.

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"So many Mustangs, so little time..."

 

I was going to check the timing yesterday(which I have never done), and I couldn't find any numbers on the timing marker. All there I saw was 2 or 3 smaller teeth evenly spaced and then one large tooth further away. I was thinking the larger one means 0*, and have no idea what the others mean.

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86 IROC-Z
Stock LG4
700R4