4 Wheel Drive/SUVs: Rough Idle

Question
> '96 Grand Cherokee, flathead 6, 4 wheel drive, automatic w/156,000 miles < Engine has a less than smooth idle;
it is most noticeable when in Drive, and at a stop. Can feel the roughness through the brake pedal. At highway speed(s) however, and this might just be due to the higher rpms, the engine seems to run smoother - no hesitation or misfires.
Have cleaned out the air-intake throat, replaced air-filter, plugs, wires, rotor and cap, but that only smoothed out the 'roughness', and made it less intermittent.
My mechanic has "suggested it might be", bad valves... $1,000 valve job to find out if it is or is not the problem??

Answer
Michael,

First of all, there is no such thing as a flathead engine anymore.  They were done away with in the late 50's or so, so if the mechanic told you that is what it is, then it's time to find a new mechanic.  You should have a 4.0 high output 6 cyl.

You don't do a valve job just because in Might Be a valve problem.  Any competent mechanic can test this by doing a compression and a leak down test.  Many things can cause this problem from dirty/bad injectors, dirty fuel filter, bad fuel pump, throttle position sensor, idle air control valve, etc.  All of these things can be tested before you replace them.

I would suggest you take it to another mechanic and have them do a complete diagnostic on the engine.

Carl