I've got an '89 Century (3.3L) with only 35K mi., relatively new PCM (engine computer) and otherwise in excellent condition (little old lady special). Runs like a champ, except when idling in Park or Neutral idle becomes rough and sometimes stalls. In gear no problem idling. Also some strange clicking/clattering at this time, possibly problem with injectors? I'm trying to DIY (myself, that is), and wonder if something like the IAC, EGR valve,or TPS could be causing the problem (or any other sensor/driveability control), therefore worth easily replacing myself. I've got a Haynes manual to help. Any clues? Thanks for reading!Edited by: whacker

 

I don't think it can be a TPS sensor. Often EGR valve can cause some
problem like your. You can try to unplug it to see if it help (but if
the valve is leaky when close you will see no difference).



You can clean the Air intake and use a strong injector cleaner. They
are easily indentifiable because they are alway in metalic coated
bottle, never in pure plastic. Also check your air and gaz filter.

 

Thanks, I'll check that out. I assume when you say unplug it, you're referring to its vacuum connection? If so, should I plug that up so it doesn't affect the engine?

 

You're right. If your EGR valve is a vacuum activated you must cap the line.

 

erakiel...do you think it might be a tranny issue, like the TC isnt disengaging all the way, so in park od neutral the trans is still partially engaged, thus dragging the engine down to the point of stalling?

 

Whacker does'nt mention any trouble idling on a gear, only at park or
neutral. In almost all case TCC LockUp will stall the motor on gear
when making a stop.



Also TCC Lockup only engage itself after the last gear normally.

 

New information.


Lots of time has gone by since my last post to this, but I've had time recently to poke around under the hood of my Buick. I've got a Haynes manual, but a significant mystery has confronted me: I can't find the EGR valve on this engine! There's no diagram of my particular 3300 (3.3L) engine, but believe me, for a car of this year, if there is one, it should be a solenoid controlled vacuum device, right? Like a little flying saucer, very common on cars up until the electronic linear type valves became standard. Well, I just see no evidence of one, and I followed vacuum lines, looked at the VECI sticker (nothing EGR there). So if anyone knows this engine, clue me in. This version has its coil pack up front (meaning near the grill) on the passenger's side. Also, the PCV valve is tucked (stuffed, really) on top of the intake manifold virtually under the generator (passenger's side). Can't imagine how to get at that when necessary. Totally unlike any pictures I've seen. But anyway, it's logical to think the EGR valve might be a possibility when idle is rough.


Another clue for you t-shooting sleuths: The idle is NOT rough when the A/C is on (even in Park/Neutral)! Therefore, I submit that,when A/C is on, theECMis making an adjustment to the idle air control (IAC valve) to counteract the load and maintain idle speed. When this load is taken away (A/C off), maybe either the IAC is not returning to proper position, or perhaps the throttle position sensor is not good, or maybe both. Had a Ford Escort with weird idle problems once and the dealer replace both and fixed it. So what do you think, and how could I troubleshoot it further? The IAC is pretty easy to obtain and replace, but the TPS might be trickier, due to the alignment that may have to be done with the throttle plate. Any opinons or ideas? Lemme have 'em! And thanks!

 

Here are some things to check. Try cleaning the throttle body, IAC motor and the orifice in which it operates. Also, the EGR on this vehicle is completely electronic, and as I recall, it has some three connections on it. There is no vacuum to this device; it operates completely electronically. Let me know... Ray

 

Hey Ray,


Thanks for the reply. I've gotta tell you, I thought I was familiar with EGR valve types. I've been working on a '99 Saturn (my primary car) that has the electronic (linear, as they call it) valve, and regardless of location, I've looked at everything under the hood of my '89 Century, and nothing appears to be there that I can't identify. And isn't it kind of early in the evolution of emissions devices for an '89 to have that kind of valve? Saturn didn't start using the non-vacuum type until '95 or '96, I think not until OBD II came along. Maybe there was a different technique used with the 3300 engine (or at least my particular version) to take care of lowering the combustion temperatures and reducing NOx emissions. A very strange possibility, but the top of my engine does not have the vacuum EGR as pictured in my Haynes manual of a "typical" 3300 engine, and I've looked all around it, usually with emphasis on things close to both the intake and exhaust manifolds. So I'm stumped on that issue. But I do think the engine could use a throttle body cleaning, and the same with the IAC valve. The fact that turning on the A/C clears it up is intriguing, don't you think? Thanks for the advice, please keep it coming, and I'll report anything I come up with. Having an official Buick factory service manual handy would be nice...

 

Since the complaint seems more involved with a rough idle, I suggest looking at stuff involved with idle quality. This involves DIS systems, fuel delivery etc. Try listening to the injectors, looking for one sounding different. You might also look at the ignition coils, for a dead pair. On the early units, as I recall, the spark plug leads on the coils were adjacent to each other. If so, try disconnecting the plug wires and see if a spark jumps between the connections on the cap. If so, they are ok. If not, you could have a defective coil. Try switching coils with a good one, noting whether the problem moves. If it does not move suspect the module. If it does move, the problem is likely the coil.IAC problems do not typically create rough idling. Ray