On my 89 TBI, I get some vibration at idle. It drives fine. The only problems I've noticed is once in a blue moon, when I've been driving. I park it, then get back in and start backing up. The car would die. But it hardly ever does that.

With regards to the vibration, which is my concern. It is kinda hard to explain. But it sounds like something trys to kill the engine for a split second. Like someone chokes the engine for a split second. I can feel it when it does it through the steering wheel and the floor pan. And I've noticed when I feel/hear it that I can see the tach drop for a split second in sinc with the stumble. You can also hear it at the exhaust pipes.

It doesn't sound like something is knocking. It is the sound like it is being choked, but just for a split second at a time. I guess you could call it a slight stumble, but isn't as noticable.

Any ideas? Its been like this for years. Car has 160k miles on it. I've replaced the spark plugs, wires, cap, rotor, O2 sensor, EGR valve, coolant temp sensor, coil, fuel filter. And it still does it.

I have had the cat removed, and the emission stuff removed. Could that have anything to do with the slight stumble?

 

Vacuum leak maybe - check all te vacuum lines and around the intake area for vacuum leaks.

 

I've looked before and couldn't find any. I did get a vacuum tester pump thing to check and make sure some of the lines would hold vacuum. But I couldn't test all of them that way.

I'll have to go look at it again as I'm sure there are alot of vacuum lines. What is a good way to check for vacuum leaks?

 

get a can of carb cleaner and spray it around all the vacuum fittings and around the intake while the car is running - if you get a smoothing of the idle, or an increase in idle - that's the area where the leak is.

BE CAREFUL with the carb cleaner - it's combustible - you don't want a fire! Just light spurts here and there to see if idle changes.

 

Would throttle body cleaner work? I do remember doing that to the TBI base, and I noticed no change in idle. As years ago, I did pull the TBI off to clean it and the IAC. Which I've since cleaned the IAC again.

I do have an open element. So, I have one of those ports blocked off at the front of the TBI that is supposed to run to the diverter that causes warm air to go to the intake at startup to get it warmed up faster I believe.

 

I read in my Chilton that the IAC is maintenance free. It pretty much said to leave it alone and if you need to replace it you need to adjust it just right because it's sensitive.What about your knock sensor? Make sure to keep me updated because I'm having similar problems.

 

I just cleaned the IAC as I've read it is a good idea. I cleaned it like 8 years ago when I had the TBI off. And I cleaned it again a year ago just to see if that would do anything.

I don't know about the knock sensor. But I figure if that was a problem, I'd get a code. Or would have problems driving, which I have none.

Just a slight stumble at idle I guess after the RPM's come down from a cold start. It sounds like "Doomph" when it does it and I can see the RPM's dip when it does the "Doomph". So, I assume it is a stumble. I don't think it is a miss, cause I've had a miss before due to a burnt spark plug wire. And that was pretty constant and was noticable while driving. Where as this "Doomph" comes and goes only at idle. Sometimes it will be just one "Doomph", then a few seconds later I'll get another "Doomph". And sometimes it will be a group of "Doomphs".

Next time I have it at the shop, I'll let them watch the RPM's to see if they have any idea. But I know it affects the RPM's, and you can hear the "Doomph" at the tail pipes.

 

timing?

 

It's at 6.

 

And I had replaced the harmonic balancer. I noticed the rubber on it was bad. And it wabbled some. Replaced it hoping it would fix it. But I noticed no difference.

 

everybody thinks that just because someone says 6 is where to set the timing

loosen up the dissy so that it is hard to turn but will turn

drive it and advance it untill you get spark knock- small increments

back it off untill it goes away

drive it untill it gets to op temp

shut it down and try to restart it after 5 min

if hard to start back the timing off a little untill car starts normally

then take out the timing light and see where you want to set timing from now on

 

I don't think I'm gonna go through all of that. The factory timing is 6*. I had it set at 6* a year ago. I checked the timing a few months ago and it was still at 6*. So, that should be fine.

 

to each his own

 

factory timing setting on a TBI car is 0*BTDC, not 6.

 

I had thought it was 6* for year 89. I too had thought it was 0* years ago, and I had taken it in to a shop for them to check and set the timing. They looked the specs up in their computer and said timing was 6*. I told them I read it was 0* and had them set it to 0*. It ran at 0* for years. Later on is when I read timing had changed to 6* in 89. Then a year ago, I had a shop set it to 6*. It still runs the same.

From what I remember reading years ago, timing was 0*, then changed to 6* in the year 89.

 

Timing is already at 6*. I don't really think I should raise it any higher anyways. Besides, I've never read your way of setting/checking the timing before. Maybe thats for a custom racing engine?

Mine is just a stock engine, so don't really see the point in second guessing the timing as the factory already has a setting for it. Kinda like how they have a factory setting of .035 spark plug gap.

 

when the factory timing chain gets alittle stretch you need to compensate by using my method