Engine Runs Rough @ 1 to 1.5k RPM, Advice Greatly Appreciated
 

Hello all,

Despite the fact that I've had my FD for about 4 months now, I am still experiencing the exhilaration felt by a new owner of a long-desired automobile. I have come to love, appreciate, and actually care about my new car to a much further extent that I formerly would have considered reasonable. I've been intrigued by the FD since I first knew of it, and I now know firsthand why these cars have such a strong and loyal following among those lucky enough to have acquired one.

That being said, I am experiencing what seems to be a relatively minor issue, though perhaps it is indicative of something major. This is what I am hoping one of the more technically inclined will be able to assist me with. I did try to search for previous solutions, but I did not find anything quite like my problem.

First, about the car:

1993 Touring, manual trans, 35.5k miles, completely stock except short shifter.

Now, the problem:

As the title of the post suggests, my engine runs pretty rough in the 1 - 1.5k RPM range. When I first start the car on a dead cold engine, it will do the high-rev thing (though I've read that this is bad and have since been putting it in 1st to circumvent that feature), the engine will start its idle at 1.7-1.8k. As it warms up and the idle decreases to slightly below 1.5k, the motor seems to operate erraticaly, and the whole care slightly shakes and vibrates from time to time. This behavior seems to get worse as the idle RPM decreases towards 1k.

Once it hits 1k, or very slightly below that, the idle smooths out again and feels perfectly fine. Once fully warm, the idle steadily remains at 700-800 RPM.

Also, I have noticed that after the engine is full warmed up, if I rev the engine to somewhere between 1 and 1.5RPM and then let off the gas, the engine will get that "stumbling" feel to it and cause the car to slightly shake as the RPMs drop through the problematic range. Additionally, revving it to between 1 and 1.5k and then letting off will sometimes cause the exhaust to make a popping sound. It could be a backfire, though I honestly don't know enough to say for sure.

I'm hoping this exhaust noise is due to one of the two other problems I know of with the car. First of all, the stock exhaust is completely rusted through in one area, and there is about a 4-5 inch rip in the muffler. Also, my rear suspension clunks quite a bit, which my research indicated is almost certainly the pillow balls, but I can't see how that could possibly be related to the idle.

One more tidbit. Though the weather got pretty cold by me shortly after purchasing the car, I am fairly certain I did not have this problem in warmer weather. However, I can't recall for sure. The problem might have been present all along and was just exacerbated by the colder temps, or it might have just taken me awhile to notice.

I'd greatly appreciate anyone who could steer me in the right direction. I suspect the logical course of action is likely glaringly obvious to you knowledgable types, and I can't express enough how valuable the information that is second nature to some of you is to newcomers like myself.

Thanks in advance,

Jim

Pull the engine codes to see if the ECU has anything stored that would tell you if it is a faulty sensor (water thermosensor, IAT, etc). There is a "how-to" on our website.

Checked the intake filter lately?

It's fairly normal for the car to "spit" during the cold idle. The car runs rich when cold (as do all cars) since a cold engine atomizes fuel poorly.

I'd also make sure you've covered the tune-up bases - fresh plugs, fuel filter, good plug wires, etc.

Dale

first i would check for codes. second i would do a tune up.

just thought about it... your tps could be bad. one way to check would be to backprobe the green/red your looking for 1.00v with the throttle completely closed. 4.99v wide open throttle. then switch to the solid black wire. you need .4v completely closed. 4.3v wide open throttle. hope this helps.

-Lance

actually the tps sensor hose could be split or popped off all together.

certain portion of description it's normal :)

your stumbling... adjust your bleed screw could help it alot.

your exhaust.... change it :P

i have the EXACT same problem...car kick in the 1-1.5rpm range....surges and shakes like a cam'd v8 on start up...idle clears up to 800 perfectly after a few mins

i guess ill check my tps and my bleed

Throttle position sensor, or you could be running rich at idle. if you try both, and get no results, do a compression check.

any results guys?

im interested too