When Technicians Just Guess What's Wrong

My 96 Buick Regal has been getting these spells many times where at idle at a red light the engine gets to rolling, going chug, chug, chug, and the car begins bobbbing up and down with the loping of the engine. The exhaust during these spells smells like a Coleman gasoline lantern as you turn out the flame, I always thought it was incomplete combustion when a lantern smelled like that. I sometimes get a trouble code that says “random ignition misfire”. I had it analyzed by a shop for $80 and they said “it might be the computer” but could find nothing definite that would cause this chugging, and lower gas mileage in a lot of stop and go driving with a lot of time spent at idle. So I bought a new computer, had it flashed, and this cost $211. But the problem is still as bad as ever. I have wasted about $300 and the technicians were only guessing that the computer was bad. Does anyone know what could be causing this chugging problem? I read once where a rich idle will cause the engine to roll. I would think though that it would smell more like raw gas than like a Coleman Lantern being extinguished?

I’m more thinking towards a bad ignition module. Incomplete combustion due to no spark is just as bad as an over-rich condition. But an over-rich condition will set a different trouble code. If you have not had it done yet, I’d have the ignition module and coil paks evaluated. These can be tested off the car, and if not within specs, replaced. If they check out, there’s a cheap way to check the injectors. Use an automotive stethescope to listen to the injectors pulse as the car idles. Any injector that sounds different is suspect. You can try a good fuel injector cleaner to try a loosen it back up. If that doesn’t work, you may need to replace it.

The problem might be cause by a leaking fuel pressure regulator. If the regulator is leaking, this will introduce unmetered fuel into the engine. This will cause poor fuel mileage, looping at idle, and a gas smell out of the exhaust.

Here’s what the fuel pressure regulator looks like http://www.autozone.com/shopping/repairGuide.htm?pageId=0900c15280067f41. Remove the vacuum hose from the regulator, and gas leaks out of this connection, replace the regulator.


To fix a misfire, it may take doing a dozen different things. Since most people, including many “mechanics”, are looking for that one-shot cure, doing a dozen things is substituted with throwing (expensive) parts at the problem; or, you’ll be told by “mechanic-without-a-clue”, “OH, it has to happen with us before we can find the problem”. Even for mechanic-without-a-clue, the car maker has drawn up trouleshooting charts to aid in finding, and fixing, problems with the engine computer and its inputs and outputs.

You need to do a few things to bring your car to a good tune, before anything else: replace spark plugs and wires (if not recent), air filter, fuel filter, pcv valve, and any other routine maintenance items.

Clean the engine intake track for optimum performance with an MAF Cleaner, and a Throttle Body Cleaner for the throttle plate, throttle bore, and the idle air control valve and its air passages.

The engine behavior changes at idle, sometimes. Why? What could change? Well, several things, like the egr valve, or EVAP purge valve opening/closing; or, the engine control system changing from closed loop operation to open loop operation. The engine can change to open loop operation if the engine has idled long enough for the oxygen sensor to cool below its operating temperature (about 600F degrees) in the exhaust. In open loop, the engine computer controls fuel and air through the iac from table … not, from actual values from the oxygen sensor (which there no longer are any).

When you start driving the car, again, the exhaust gets hot enough for the oxygen sensor to begin operating again, and the engine computer resumes controlling the fuel flow (etc.) from active input sources; thus, the engine runs smoother.

If I were to make a swag, I’d consider changing the oxygen sensor on suspicion
that it has become old and slow (and, it’s relatively cheap) AFTER I did the other stuff FIRST, and still didn’t git no relief. http://www.autozone.com/N,16100117/shopping/partTypeResultSet.htm

Thanks for these comprehensive replies. I began suspecting sensor problems, and began disconnecting them to see if there was any change in idle. None until I disconnected the first sensor in the air intake track, a flat device next to the air cleaner. The engine immediately idled smooth. When I reconnected it, it started chugging again. Is this the mass airflow sensor? If this is at fault I can’t figure out why the shop wouldn’t have been able to observe what I did!!!

This link shows the MAF (Mass Air Flow) Sensor, and how to test it: http://www.autozone.com/shopping/repairGuide.htm?pageId=0900c15280067e26 You would do these tests AFTER cleaning with the MAF Cleaner.
If you think that disconnecting the MAF, “and the engine runs smoothly”, is enough of that “testing stuff”, and you want to change the MAF before doing any of the other things responders have advised, suit your self. If not, go back to step 1.

I took the car back to the shop today, and they said that when they had analyzed it a short while ago, it wouldn’t show it symptoms. Today it did, and the mechanic used a diagnostic device on the engine and determined an improper frequency output of the MAF sensor and said it definitely needed to be replaced. I bought a rebuilt for it, and the car now seems to run ok, no engine rolling as with the faulty MAF sensor. But the service engine light won’t stay reset, keeps bringing back a code PO102 of “low input”. I’m wondering what additional issues my car is having now.

These are some of the things the technician needs to check: http://www.obd-codes.com/p0102