1995 Buick Park Avenue Ultra rough running

I bought this car last November with 145,xxx miles, now has 165,xxx. The CEL has come on since my purchase, and my mechanic (retired from Buick dealer) said it was no big deal, as the car ran great, with no apparent issues. Not the case any longer. I still haven’t found anyone to read the codes due to the OBD 1.5 (and I can’t afford the dealer fees). The CEL light seems to come on after driving a few minutes, and after letting up on accelerator. So here are my issues:

I was getting 23-26mpg with mixed driving, car loaded (large family, school car), now we are getting 15-17mpg. The car is now sluggish, even though I always use premium fuel from places like Shell.

Bucking - While in OD, acceleration, either to going uphill or increasing speed gradually, causes a slight bucking. This goes away when the car is kicked out of OD. It has done this both when otherwise running smooth and now under rough conditions.

Surging - began a few weeks ago. Engine revs (at low rpm, on its own) to above 1000-1500. This makes stopping or parking a problem, as the car is harder to brake or surging. Has gotten worse, as it acts like cruise control, maintaining speeds as the the rpm is around 1500.

Idle/rpm issues - Now, rpm will start going up/down quickly, usually after letting off the accelerator. It will suddenly drop to 500 then up to almost 2000, and go back and forth. Pushing down the accelerator will break this cycle. Idle can be pretty rough at times.

Tranny OD - Transmission was rebuilt by a local, reputable shop. This problem happened before the rebuild (15k miles ago) and still occurs. It is intermittent. As the OD (or torque converter) kicks in, it seems to “thud” into place. This is more a feeling than a sound. It happens about 50 mph, and the rpm drops. It can clear up and come back with no apparent reason. Aggressive driving seems to clear it up, as cruising down roads at 50-60mph speeds are when it’* noticed.

Here are repairs made to car since I’ve owned:
AC compressor
Radiator/thermostat replaced
starter replaced
tranny rebuild
several tensioners and belts replaced
recently one plug wire (don’t ask me why he only replaced one, lol) due to rough idle, cleared it up for a week


Here'* where I am now....

I removed Mass Air Flow sensor, sprayed with CRC cleaner, let dry.

I sprayed CRC TB cleaner in the throttle body (with the AMF sensor removed) and cleaned a majorly gunked up "butterfly". (I will be removing throttle body and thoroughly cleaning asap!) This alone made a major difference in the drivability of the car!!! For the first 30 min after, no surging, no high idle, no idle fluctuation, etc... Still not as smooth as I'd like but way better than before. After 30 or so, most of these symptoms returned, but much milder than before...

Next day, I replaced all wires and plugs with AC Delco plugs and NAPA Belden wires. Once again, improvement. No bucking while accelerating in overdrive. Car starts fast, runs fairly smooth for at least 30 min before any high idle or such. However, I feel that the car isn't as peppy as it should be, just a bit sluggish most of the time.

And here is what I found today. I was able to get codes read this AM... It is registering P1670. Could that explain anything that I have described with the car?

My preliminary findings are that it is Quad driver circuit 4. Most guys that I am seeing on forums say that putting new ECM in car isn't always helping, but a short, bad fuse or relay, etc...

The shop that read it for me wanted $275. $100 for used part, $100 for dealer reprogramming it, and $75 for labor, with 6 month ward on parts and labor.

I appreciate any help! Thx...

I have the same car, and mine did some of the same things you mentioned, it ended up being the Throttle position sensor. It was a $50 part and took maybe 35 mins to change out (its on the bottom of the throttle body just easier to remove throttle body and change it that way) That could be your issue, just a thought. Mine keeps throwing a Quad driver 1 code every now and again but it hasnt shown any issues.

I agree, it sounds like the throttle position sensor. Read this:

Part 1 -Throttle Position Sensor (TPS) Test: GM 3.8L (P0121, P0122, P0123).

Ok, will be replacing the TPS... btw, 2kg4u, that site was great! Never been there before, def bookmarked..

Opinions on the brand of TPS? Napa has Delphi at $90, their brands at $50... Autozone at $50.. Anyone?

Im running one from Oreilly'* in mine with no complaints, I got their cheap $50 store brand one. Put it in and it works great!

You could also check the metal EGR tube going to the bottom of the intake manifold. I think a P1670 will also point to that.

ever figure out the problem? I had problem with tps on my 95 lesabre, kept sticking, cleaned it up and it worked just fine, but I already had ordered the part and it was relatively cheap, so i put a new one in anyways..........also had A LOT of issues with the vacuum regulator deal on the trans...sadly i replaced it with a FRAM as the price difference was ridiculous 16 compared to over 100...and it worked but just before i mostly retired the car it started popping out of OD again randomly...i suspect further transmission issues that I did not care to deal with...now I am plotting to make it into a snow plow with the studded tires I only got one lame excuse for a winter out of.