I have no clue..

See if you have any codes over time from driving.

If there's no codes, I'd say take it to the mechanic for a diagnoses

 

Check the fuel filter as well.

 

If it's fuel related, or you think it might be, I'd replace the fuel filter just in case (unless done recently) since it's fairly cheap and easy on that car. If the bucking was spark-related, my first guess would be the ignitor (a.k.a. ignition module). If the car ever stalls, check to see if the CEL is lit up - if so it would lend credence to it being the ignitor, which may or may not leave a code behind when you check.
When it bucks, is it under acceleration or when holding a steady speed? I can't say this is always the case, but in the past when I've experience fuel problem bucking, it was under accel. whereas when it was a failing ignitor (very rare, sporadic, lasted a very long time despite this) it was normally when holding a steady speed, right after I'd stopped accelerating, and had shifted into 4th or 5th to cruise (plus once at idle which lit the CEL but no code).

 

Thanks for the replies.

What I have done so far:
New plugs
New Wires
New Fuel Filter
Reset ECU
Used Heet & Injector cleaner

Since my last post, I have had several days and a few hundred more miles with which to become familiar with the problem:

The car idles and runs steadily down the road as well (or better) than it did before the problem appeared, but the bucking/hesitation still occurs frequently when taking off or when pressing swiftly on the accelerator when driving. This occurs no matter what engine temp or speed, and no CEL messages have appeared. Also: the car is not starting well at all, it used to start on the first crank, but now takes several seconds of cranking, or more, to start.

The bucking has also increased in frequency in the last few days, which reminds me ....on a side note... I have almost cycled through an entire tank of gas since this problem appeared, and am wondering whether the fuel treatment (heet/cleaner) that I used may have temporarily soothed a rich or lean mixture problem, if I have one.


Added notes:
I never thought to mention this, but this car has experienced a few changes recently that might affect a diagnosis. Six months ago it had a new timing belt installed, and a few weeks ago it was impacted hard enough on the right front wheel to require a new right wheel and suspension components; neither of which were performed by me.

 

Did you get a chance to check the coil and ignitor while you were in there?

 

Update: I either found & aggrivated the problem or caused a new one.

Before buying a fuel pressure gauge, I took your advice and went into the distributor and found a lot of corrosion on the cap terminals and some black residue on the rotor contact. I cleaned completely, but the rotor contact looks to be out of round... looks like it has been arcing for a while.

The coil tests within parameters for primary & secondary resistance as well as for internal grounding.

I cleaned everything with wd-40 and put it back together, but the car would not even try start.

Cap and rotor are not available until Wednesday, but I would think that I would have SOME spark even if my cleaning of the contact points increased the arcing distance. I am afraid that my Wd-40 may have gotten too far inside the distributor and causing problems.

New symptoms - car wont start at all, and now there is a new high pitched humming coming from the firewall area when the key is left on after attempting to start. I poked around with a screwdriver to my ear and can be confident that this hum/whine is coming from something attached to or inside the motor... the noise is most noticable when touching the intake manifold.

 

POSSIBLE RESOLUTION, but won't know till Wednesday.

I took my distributor apart piece by piece to clean and look for bad connections. While the coil was out, I decided to test it again... and even though it tested fine earlier, it is testing horribly now.

Primary Resistance - 1.0 - 1.1 ohms ... about 10% higher than spec
Secondary Resistance - 7000 - 8000 ohms ... more than 50% lower than spec.

Also: I read a very interesting article that claimed the actual ohm values are not what are important, but the ration between them. On a "spec coil", the ratio would be ~16,000 (13,000 / .8) and on my coil the ratio is less than 8000 (8000/1.1). Very interesting stuff.

Hopefully I will have good news when the parts come Wednesday.

 

Arcing from the rotor to the cap is normal. The rotor does not touch the cap terminals as it rotates, so the spark jumps the gap. This arcing slowly wears the contacts down and this is why over time it needs to be replaced. It could be a bad coil. The wd-40 might not have been the best to use for cleaning, there are some sensitive parts in there. I would clean everything out with some brake parts cleaner and reassemble it, then try starting it again. As to the humming you are hearing, that would most likely be the IAC or Idle Air Control valve on the rear or the intake manifold. It is a frequency modulated soleniod; and on failed starts it will sometimes hum like that because it's trying to adjust air flow to start the vehicle. If you turn the key off and then back on, it should go away.

 

RESOLVED!

So my rotor, the distributor cap, and the bad coil were all replaced today and the car runs as good as it ever did... I forgot how peppy it once was.

It did throw another CEL on the test drive (oxygen content), but I cleared it and the CEL never came back... I am hoping that the ECU just hadn't adjusted to the more efficient ignition or something... :/ But no mater what, it is running perfectly.... and it looks like I might be back into 30+ mpg! :thumbup:

 

Congrats.