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Bucking at low speed

Hi. I have a 1992 SL2 Saturn. It has 107,000 miles on it. For the last 20,000 miles or so, it has bucked on acceleration, particularly when warmed up. (It bucks when cold, but only mildly, and because the idle is up higher, the bucking is masked.) At highway speed I can sense a miss, but the speed of the vehicle smooths out the bucking, and it is hardly noticeable - but it is there. I have replaced the plugs, used several bottles of injector cleaner, replaced the in-line fuel filter, resistance-checked the spark plug secondary circuit, verified that the fuel pump is within tolerances published in Haynes, and verified the proper operation of the EGR valve and fuel manifold pressure relief valve. I have also replaced the accelerator cable. The "Service Engine Soon" light is not on. There is nothing logged on the car diagnostics computer that I can find. The car may be getting about 2 miles per gallon less than it did

20,000 miles ago, but I can't be sure - it gets about 28 mpg today, combined driving. I don't know if this is related, but when I engage the cruise control, there is a temporary increase in engine speed and road speed (to the tune of about 4 mph), before it settles down to the selected speed. (Settles down in about ten seconds.) Cruise works perfectly after that. I am lost for ideas. Anyone got any ideas?
Reply to
rslakey
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did you replace the air filter? maybe that's clogged, or your throttle body is fouled or something like that - I would try removing the airbox, cleaning the throttle body (make sure the plate is clean on both sides, and operates smoothly - carb cleaner works well for that), then reinstall the airbox with a new air filter. Also, if there is some sort of aux. air valve/idle air valve/etc. make sure it is functioning properly and not fouled (also make sure the intake leading to the air filter isn't plugged with leaves or something like that). Another thing to check would be electrical connections - I would de-mate, clean, and re-mate all of the connectors you can find, then disconnect, clean, and re-connect all of the ground connections (not uncommon for oxide buildup or other crud to increase resistance and mess up electrical performance in a car - esp. after 11 years!). Could also be a bad injector... Another potential issue - if the car uses a MAF sensor, it could be fouled and need to be cleaned (clean the wire very, very carefully).

Reply to
David & Caroline

You too? My '93 SC2 is doing it too. I've yet to try plug wires, it seems ignition related. I'm wondering if it's the MAP sensor - my harley did this when I once unplugged and didn't replug the sensor, but on the saturn, I don't know if MAP affects the ignition...

Reply to
Philip Nasadowski

How old are your plug wires? That'd be next on my list.

Reply to
BANDIT2941

This is likely an ignition problem, such as voltage leakage from the plug wires, or carbon tracking of the ignition coil(s)..

Reply to
Robert Hancock

That reminds me. I had a coil go once, actually it might have been the module, I'm not sure(I replaced both coils and module with a unit from salvage yard). The car bucked like crazy. Like I said before, try spark plug wires first. They aren't that much $ and by the sounds of things you might be overdo for a change anyway(ie, if they don't fix the problem, you didn't waste your money). If I may suggest, get a set of Accel wires from NOPI online. I think they were either $26 or $29. All the plug wires I bought from stores like NAPA and Autozone(and I tried like 4 or 5 diff sets) leaked voltage after a month or so. The Accel's are cheap and so far are holding up good.

Reply to
BANDIT2941

Reply to
Dan Hicks

Hello to all those who had ideas. I have replaced the wire set - no help. I also forgot to mention that I had replaced the EGR solenoid for something else - a code 26 at speed. Anyway, I also verified the operation of the injectors - all are clicking, and not missing a beat. I decided to go for broke - a replacement of the oxygen sensor. That fixed it. Smoothed right out, and power is back. Thanks to all who provided insight!!

Reply to
rslakey

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