[bocoogto]

My '93 Roadmaster has a stock 5.7 Chev engine. At light loads (around 1500-2000 rpm), the car bucks as though there is an ignition miss. At lower or higher speeds, this is not noticeable.

Plugs, cap, rotor, and wires have about 20,000 miles on them. The only thing not set to factory spec is timing. Book says 6 degrees with the electronic advance disabled. I've set it to about 10 degrees in an attempt to improve highway mileage. Problem did not occur until about a year after setting timing as described.

Any ideas?

 

[bocoogto]

Tried setting timing at 6 degrees as recommended. Engine bucking or miss is still the same. Plugs and cap & rotor have about 25,000 miles on them and look very good.

Any ideas?

 

[bocoogto]

Problem is getting worse. At about 45 mph in overdrive, it's very noticeable at times.

 

[Fuzzy from MN1988]

I can't believe noone has commented on this... I would look into getting your computer screened. You can have that done at just about any parts store. I always go to Autozone and they're willing to help out. Maybe look into the fuel system?? When's the last time you changed the fuel filter? Injectors maybe, I had a car that bucked quite a bit and was slow taking off when it had bad injectors. I could tell by going to different gas stations which one had better gas. I'm at a loss on what it really could be.

Have you tried cruising around in D? Your last post said you were doing 45 in OD.. Maybe something with the tranny?

I'm no mechanic just trying to help out..

 

[bocoogto]

At the suggestion from another forum for a similar problem, I disabled the EGR valve by disconnecting the vacuum line and blocking it. Problem is gone.

Now, I'm wondering about the downside of having no EGR. If the only consequence is worse emissions, I'll leave it as is--disconnected.

 

[bocoogto]

Since disconnecting the vacuum to the EGR, the Service Engine Soon light comes on occasionally. It stays on until the engine is shut off and restarted. Then, when driving about 60 mph with engine fully up to temp, the light comes on again.

All aspects of driveability are OK and the original jerking or missing is gone.

 

[bocoogto]

I bought a replacement EGR valve. After installing it and hooking it up, the problem has disappeared. No check engine light, no bucking. Easy fix for $49.50!