[Dick Boneske]

I've posted on several Buick sites with no answers. Car is a '93 Roadmaster with factory 350 Chev power. Car runs great--22-24 mpg on highway, good power, good idle. Problem is at about 1500 rpm in overdrive---40-50 mph--the car surges or "bucks" as though there is an ignition misfire. No "Service Engine Soon" light.

Plugs, cap, & rotor have about 20,000 miles on them. Plugs run a nice light brown color.

Any ideas?

[mike nixon]

93 is a TBI car correct?

Unhook the EGR valve and see if it still bucks. If it does you've probably got a plugged vent on the EGR solenoid.

Also check for convertor slippage / shudder. If it's shudder there's a product called Lubgard that works well for this issue.

[68gtoMN]

If converter shudder, flush after running trans aid type product

[fbrown]

On LT1's EGR value failure would cuase the problem. The EGR failed partially open and would lean the mixture out to much. Intake gakset failure also would foul/partially foul a plug and also cause the same sympton. I'm not sure if either applies to your engine. I have had both problems in my 96 Roadmaster Wagon.

[goatwgn]

Originally Posted by fbrown

On LT1's EGR value failure would cuase the problem. The EGR failed partially open and would lean the mixture out to much. Intake gakset failure also would foul/partially foul a plug and also cause the same sympton. I'm not sure if either applies to your engine. I have had both problems in my 96 Roadmaster Wagon.

TBI setup is different from LTI. The EGR can lean out the mixture on any engine, however, regardless of make. It will create a good sized vacuum leak if stuck open. I would also check the ignition module, and although you installed new wires, make sure they are a good brand and are routed correctly away from the exhaust as much as possible. I have seen brand new spark plug wires misfire that people have brought into the shop where I work. Drive the car in drive (or 3rd) gear at the same 1500 rpms and see if it still "bucks", ensuring that it isn't an internal transmission problem with the 2nd/od clutches, etc. Good luck. I know these kind of problems can be frustrating to track down some times.

[mike nixon]

One other thing to check, be sure the shaft is tight in the distributor and not saturating it's internals with oil.

[BR57]

My 93 Fleetwood did the same thing. It is the transmission hunting. My car has 300,000 on it so all I did was pour in some Lucas Tranny Fix and I don't use Overdrive in the city anymore. Problem solved.

[gregneun]

I like the car. Mine had a tranny rebuild and did this until the tv cable was set right. Converter shudder. The egr valve is also worth checking.

Greg