1990 Buick LeSabre

I started having problems with it shortly after I bought it. It is hard to start initially, i will have to push down on the gas pedal about half throttle to get it to start. Now just recently it is missing throughout the rpm range but it is drivable. It also idles eratically up and down. I have tried new pcv valve and plugs wires, injector cleaner, with no change in performance. I have been reading the chiltons repair manual and it seems to possibly be the TPS or faulty erg valve. The comp. shows no fault codes. Any ideas?

Usually, a bad TPS will throw a code, however not always!
The TPS, is simply a potentiometer used to vary voltage. The best way to check the voltage is with a scanner, however if you don’t have one that will give you that information, you can use a DVOM. You can check the voltage on the blue wire, with ignition on and engine off. With the throttle body closed, you should have .37V to .45V. This voltage range should be ideal for idle around 750-850 rpm. The white wire is the ECM/PCM reference signal and should measure 5.0V and the black wire is ground. The blue wire should measure between 4.1V to 4.5 at WOT.
See what you have & post back.:loser:


Also, be sure to check the TPS lever, it should be "spring loaded" to return it back to the home position after throttle opening. :grinyes:

So far i checked the egr valve which looked good 24.7, 24.5, and 13.7 for ohms of resistence. tps is my next to do today in bout an hour from now...9-17-06 10:44 central time

Half throttle... hmmm mix is rich? Vacuum leak?
Does sound like a clear miss. Ignition module, coil pack? not sure of whats in your engine.
Would say O2 sensor but at start thats not an issue.
TPS can be monitored while turning it. Look for smoothness as its slowly turned.

Just participating
:newbie:

Bass

How many miles? That sounds an awful lot like a stretched timing chain. On your car, it should be done every 75-125k miles. When it is done the following should be replaced: chain, gear, damper, cam sensor interruptor magnet (GLUE IN to avoid a future code 41), and new gaskets. Not horribly expensive if you do it yourself, but it is definately a Saturday project and then some if you have to go buy tools.

Another possibility would be a vacuum leak. Check all the rubber vacuum hoses and if any are crumbly or cracked, replace 'em. How is the IAC? Has it and the TB been cleaned lately?

Well, starting is now fixed...it was the fuel pressure reg. The original still held vacuum and did not let fuel pass through but chaning with new fixed problem. now it just has a miss at all engine speeds. it only has 60,500 act and changed plugs and wires in february... they could possibly be bad but seems unlikely. checked at night in darkness while spritzing water and see no arching along wires. just put in new 02 sensor few weeks back less than 500 miles on sensor

Good deal on the pressure regulator..

Off the top of my head Im thinking.
Check the battery terminals and voltages while running.

Missing at all RPMs...

Is it a rythmatic miss? Seems like one cylinder? Not surging.
If surging.. then TPS still should be checked first...
I still worry about the coil pack.
Did you check the compression? (regular miss)

I dont think a vacuum leak would present itself at all RPMs.. Mostly Idle. but depends on where it is I suppose.
A TPS sensor would throw throttle around, like surging and such.
ERG valve has my suspicion, But suspect the O2 sensor may throw codes with it bad. Not sure there.

Try getting a coilpack. Not sure if those squarepacks are swapable but you could get junkers and see if the problem gets worse or better..
Sometimes I have shortened the spark gaps just to help troubleshoot the coilpack. Often it will fire more efficiently across a smaller gap but still is a bad coilpack.

If its your camshaft sensor It may throw a code. You can pull the connector off the camshaft sensor and try running it around a bit and see if it smooths out.. If so.. change it for a new one.. Easy job.

An injector would proubbly not give you a good idle.. Still suspect.
The MAF sensor can be carefully cleaned. The ECT sensor may also give you bad signals and give you a wrong mix. The car adjusting for cool enging then a hot one then a cool one.. etc.

IRRATIC up and down IDLE may be found by Idling it for ten minutes or so and checking the plugs for carbonizing.. and good color. It also would verify your new plug wires. Did you spray the Coil Packs.. they usually fail under load first like uphill or something.
You say Idling up and down .. is that a smooth Idle when up and a smooth idle when down, or a miss.. Spraying a little starter fluid in the intake during an idle would tell you its a Mix problem, but why it may not.

TPS still should be checked first...


Anyway. GOOD LUCK>

Have you tried cleaning the EGR passageways? Or the MAF sensor/Screen? Or the IAC valve? As for the injectors, I suggest trying a bottle of Chevron Techron (large bottle, kinda pricey but worth every drop) to clean them up. What about the fuel filter? Every 10k miles you need a new fuel filter...I've seen them cause wierd running problems after they get clogged.

As for a coil pack, if you do decide to get one, don't waste your money on a junkyard coil pack...It is difficult to find a decent used one.

Yes, the Cam sensor will throw a code. An incrorrectly calibrated TPS will not always throw a code.

At 60k is miles, your timing chain should be fine.

Take a look at my thread: http://www.automotiveforums.com/vbulletin/showthread.php?t=452655

The computer in my car was not firing the #4 injector, and causing bad vibrations and rough idle. Replacing the computer solved the problem, but make sure you troubleshoot first.