1990 Buick Century 3300 MPI Hard Start, Rough Idle, then Dies

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Hello all,
First post on this board. My brother-in-law has an old 1990 Century that is having some issues starting and poor idle. It currently is not driveable.

Basically he said a couple days ago they were driving it home and it started running really ruff and died then they ended up toeing it home. Well I went and had a look at it today it was throwing up two codes. A 21 for the TPS and a 43 for the ESTC or Electronic Spark Timing Control.

My brother in-law changed the TPS last night but wasn't sure how to adjust it. Its a three wire so I checked his Chilton and it said for that type just set it so the levers touch from the throttle and the TPS. I did that also tryed moving it around. This puppy don't want to start. So I tryed old tps wouldn't start either. Pulled a wire and checked was getting spark. So pulled a couple plugs. This thing has the Spark Control Module with the 3 coil packs sitting atop it. I tryed two plugs both on a diffrent coil. Each was black with soot and carbon. This thing is getting a ton of fuel and I looked at the airfilter its been backfiring into the airfilter a bit also before it decided not to run anymore.

Well after looking up codes I saw lots of peps saying control module so I pulled it had it tested. It was good after 6 tests in a row all good. So after reinstall started once very rough idle and rough running even when it would rev a bit. IT was sucking air in via Mass Airflow Sensor.

After we reinstalled the control module we hooked batt up again and it started and ran rough. I tryed moving module around a bit to see if it needed to be adjusted. Saw NO noticable improvments.

After that got a diffrent TPS code a 22 and the same 43

Not really sure where to go on this. Any ideas are appriciated..

posted by  x_789

1st u need to do a compression test and leakage test to make sure the motor isnt fried...
2nd we need to know mileage how long he ran it with the check engine light etc...
3rd whatever the problem ends up being ur looking at needing a new catalytic converter b/c of the amounts of raw fuel u dumped into it

posted by  Pieface

The car has around 120k on it total as for it having compression issues I dont think so. They drove the car up to the store about 5 miles from house it ran fine there. Went to come home started acting eratic. Didn't even make it a mile after it started acting up. As for the cat we will deal with that after we figure out whats up.. X

posted by  x_789

A code 22 on a 1990 Buick is low TPS voltage, a code 21 is high TPS voltage. Test the TPS and see if it needs replaced. If you need instructions, I can find a website for you which has good, detailed instructions.

http://www.autozone.com/servlet/UiBroker?ForwardPage=az/cds/en_us/0900823d/ 80/0f/18/19/0900823d800f1819.jsp is a link to a set of trouble shooting charts which may be of some help

posted by  tbaxleyjr

Well prior to a new TPS it was a 21. Then after a new tps still a 21. Then after it was replaced I cleared codes and played around a bit with the sensor and it gave a 22. I guess its possible that he got a second dud sensor but not likley. Unfortunatly all I have is a multimeter I guess I can make some jumper wires and see what I can find out by checking voltages that way.. X

posted by  x_789

Check your installation and make sure the TPS was inatalled right. My initial feeling is the TPS was not adjusted. Some TPS installations require adjustment after installing.

Use a digital meter. Key on, engine off, W/throttle plate closed, you are looking for a voltage output of about 0.55 V, wide open throttle, you are looking @ 4.5 to 5 V. Look for smooth voltage changes when you move the throttle from closed to WOT If you do not get 0.55V with throttle closed, slightly loosen the screws and rotate the TPS until you get the specified voltage with throttle plate closed.

Once we deal with this issue, we'll tackle code 43

posted by  tbaxleyjr

I have encountered the same problem. I have a 1992 3300 with 92k on it and had stalling, rough idle, code 21 and 43. I changed the tps and tried to adjust the tps. It runs pretty smooth now but I get a 22 and a 43. I'm stumped also


posted by  sn1643

I had this same thing happen to my 1990 Buick Century. I repaced the plugs and the fuel pump and screen and still no change. Got worse. I was looking at everthing people had changes with no success and wondered what is the problem. I rented a code reader and it said no trouble code present. I took the reader back and was talking to the auto counter person about it and a customer that over heard us said that he had run into this and it was the coils. Bad coils won't show up on a code reader. I changed the coils and it cured the problem

posted by  MichaelD

It runs great. It gets good mpg. 33 Driving it today. Anything that ran right once can again. This site really helped me. I looked at everything people had tried to fix their 3300. I then knew to not go to all that trouble, and to look for the next step. I found that next step and it is purring now. Trouble code readers don't know everything. Sometimes it is the basics and they won't show up on a reader. I am so glad I found this site, as it really got me on the right track. I new I had to pray for wisdom. I did and it came and now I'm driving smoothly everyday.............. Thanks

posted by  MichaelD

Push it off a cliff. You're lucky it lasted as long as it did.

posted by  smallangryneon

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