Hi everybody,

I recently got a '93 Scoupe with 118,000 miles. The engine isn't turbo, and it is the kind with the transmission and air filter on the right. It came with a few problems, but that's okay--it was free to me. What I'm doing is fixing it to give away to my old college campus minister...his family is in need of an economical car, and well, campus ministers just don't make much $.

I've been able to fix most of the problems but am stumped by one. I don't want to just throw parts at it without a good diagnosis, since that could get expensive fast. I'm new to this forum, and I'm hoping it may be a familiar problem that somebody here might recognize.

Symptoms are as follows:

1. After warming up, the engine pings whenever under a load.
2. Engine somewhat difficult to start, and when cold will die right after starting.
3. Engine idles fine once warmed up, but with just a touch of throttle, it sputters and stalls. Regardless of engine load, it runs very rough up to about half-throttle. Half-throttle to full-throttle, engine runs fine except for pinging.
4. If I drive for a period at highway speed and then come to a stop, sometimes the engine surges between low and high rpms maybe 10 or so times before idling normally.

The spark plugs are black with carbon due to the poor combustion, but not worn out. Distributor cap and wires look are relatively new. Air filter is relatively clean.

Roughness is the same no matter what the outdoor humidity, and no matter what the engine load, which leads me to think it's not an ignition problem. I suspect it is some sort of fuel-mixture problem that is triggered by a faulty sensor of some sort?

The guy at the parts store said it might be a bad throttle position sensor, and a mechanic told me it might be a MAF sensor or an EGR valve.

I've done the following:
1. I tested the throttle position sensor reference voltage (5v) and output voltage. My voltmeter showed that output voltage increased steadily from low (around .8 I think?) to high (around 4.3) based on throttle position. I found nothing that seemed unusual.

I then took the TPS to the auto parts store, and using my ohmmeter I compared the resistance of my old one to that of a new one. They behaved exactly alike. Since it's an expensive part and I could find no evidence that mine was defective, I went back home and reinstalled it.

2. I looked for some info on an EGR valve for this car, and haven't found much. I couldn't find anything at autozone.com or napaonline.com Does it not have one or something?

3. I found that a MAF sensor is expensive, and haven't found any clear instructions on how to test one, besides taking it off and looking at it. I plan to do that tonight.

Apparantly it's difficult to find cheap used parts for these, otherwise I'd have bought and tried some already. I've called every junkyard within 50 miles of Dayton. Very few have any Hyundais, and not a single one with this style engine.

Does anybody recognize this? or have suggestions of things to test and how to test them? Please reply! Thanks!