First off I am an old fb guy and this is my first fc so I'm still learning the quirks of the cars. I have an 88' n/a with some emissions removed by previous owner.


My problems started as a loping idle after I drove 1200 miles in a day and a half over the mountains. It would still run on the highway but fuel mileage dropped from 27mpg to 23. On the way back, after sitting for 5 days, it was still revving up and down at idle. I stopped at a rest stop and when I started the car again the rpms climbed extremely high without touching the gas. I shut it off and checked the throttle and it wasn't stuck so I started it up again with the same result. I tried to drive it but it would cut out at 3000 rpm and I pulled off at a gas station. I messed with the throttle and tps to make sure nothing was stuck. After sitting there for about an hour I started it and it was back to the loping idle. I drove the rest of the way back home (600 miles) with no more high revving but just the loping idle. I let it sit for a few hours and tried to start it and it revved up super high again.

I checked the tps with a dvom and it was 1kohm at rest and as you moved the throttle it rose until at wot it went out of limit then showed over 4 kohms. Good according to specs except for the little blip of out of limit every time.

I took air intake off and butterflies are closed at rest (except for outer upper ones which should be open.) They move fine with the linkage.

The last time I tried to start it it was smoking pretty bad and I really don't want to blow up the motor. Any help or ideas would be appreciated.

 

Well, any dead spots in the TPS range are not a good sign. It's supposed to increase/decrease smoothly, so if I were you, I'd replace it. Bouncy idles are almost always a TPS problem or a vac leak.

What exactly was removed emissions wise? Did the BAC get left alone, or did the previous owner think it was somehow emissions related? You've also got the AWS solenoid that works with the BAC to boost cold start idle to 3k RPM for ~17 seconds. My guess would be the throttle linkage is hanging up, or for some reason the BAC/AWS are allowing a whole lot of air into the engine at times.

 

I'll have to check tomorrow if the bac was messed with. I know what it is but the aws is unfamiliar to me. I know it's the accelerated warmup but I don't know where it is. I haven't looked at the emissions removal write-up yet to see if it was done correctly but it was driven 1200 miles the day I got it a month ago with no problems. I would think the bac and aws would be intact if it ran fine then. I haven't tried it with the tps unplugged yet and I'll triple check the throttle linkage and butterflies tomorrow. Thanks for the advice.

 

If the bac and aws are on the drivers side of the dynamic chamber then they are both gone. There is a plate blocking the port on the dynamic chamber. If these are that important why did it run fine before? With the tps unplugged it did the same thing (revving up real high) I shut the car back off when it hit 5k rpm and still climbed. I removed the throttle cable and started it and it went up to 3k rpm and ran real rough and blew smoke out the tail pipe. When it was running fine before it would smoke a bit if you went above 5-6k without warming up the engine. I figure that is oil control o-rings and shouldn't have anything to do with this problem.

 

The AWS valve would be next to the BAC, if it were there, but it's not necessary. As I mentioned, it's just part of the 3K RPM accelerated warmup system. The BAC is active for this too, but it is also used by the ECU to smooth out your idle and compensate for physical and electrical loads (A/C, P/S, headlights, etc...). I don't think it's related your problems, but it's a useful device to keep around.

If both of these are missing, there are no other sources for air other than the TB. The engine should start up and idle at 750 rpm or 1500 rpm depending on if your thermowax is still present or not. I think I'd still suspect a cable problem; maybe even the cruise control cable if you have it. It has to be TB related, since a vacuum leak big enough to boost idle that high will usually just keep the engine from starting at all, or cause it to die immediately.

 

That's what I was thinking. I was going to take the TB off and clean everything real good. There is no cruise and it still did it with the throttle cable unhooked but I'll adjust it down a little to be sure. And replace or add some vacuum caps.

 

When I took off the TB and started cleaning it I could see the secondary butterflies weren't completely closing. I cleaned the whole thing and used the set screw on the upper back of the TB to adjust the secondary butterflies closed and put everything back together. It runs as well as it did before the trip and I don't really know how it got out of adjustment. The set screw looked like it was supposed to not be adjusted. The slot was partially filled in but I was able to turn it.

 

It is strange how it just suddenly started happening, but it's nice to have it fixed.

 

Yes, it is good to be running good again. The only thing I can think of is if the linkage got bent of something like that while I was on the highway. I wasn't flooring it but was above 90mph for quite awhile. Maybe I stretched it out.