Hello Everyone. Rather frustrated as I just spent 13 hours replacing the opti, waterpump, and timing cover gasket/seals.

I had a bad idle after the car warmed up and a miss above say 4500 rpm.

The high rpm miss was present at WOT so I'm hoping the new opti at least fixed that. I won't be able to know for sure until at least Monday (2ft of snow here now). Although, it still has a rough idle when warmed up (moreso when its engaged in gear). You can kind of feel the car lunge and watch the rpm/volt gage drop and recover. Now, if you just let it idle in park you can see the rpm gage move a tad and you can hear the motor miss.

Spark Plugs are new AC/Delco gapped stock. I tested the EGR by pushing on the diaphram and it seems to be operating correctly. I've pulled my new plugs two weeks later and they look like both banks have been running rich...although I'm not getting any black smoke.

Ideas, Thoughts, Opinions???

I'm thinking it needs O2 sensors. Although, I'm not getting any Service Engine Light and I hear the 96 and newer vehicles with OBD2 pick up mostly everything. However, I did have a rather large vac leak on the PVC Valve hose and I do not know how long it was driven like this.

 

I'll just go ahead and replace both upstream O2 sensors on Sunday. This is a helluva expensive way to fix a problem (just guessing) but I'm assuming its cheaper than paying a GM dealer their $82/hr to diagnose and fix it.

If that doesn't fix the problem...I'll run it into a tree or something as I'm out of ideas.

 

You need to check all the ignition related items. About 3 of the 5 times I have replaced the opti, I later found the problem was a bad plug wire.

But I have headers so the wires burn easily. But quite often the wires will get brittle and even separate internally yet will fire a plug at low rpm but not at high rpm.

Perry

 

check your fuel pressure. a bad pressure regulator can cause an engine to run kinda funny and miss i the higher rpms. stock pressure should be around 40-45 psi

 

"bad idle after the car warmed up" says O2 sensors loud and clear.

 

I agree that it is expensive to buy parts to throw at a problem. you can take your car into your dealer and pay him the $82 to diagnose it and than take it home and do the work yourself. If you are uncertain what the problem is that can be most helpful and cost effective.

Perry

 

Ok, I got to drive the car a while today. The high RPM miss is gone and it seems a lot stronger and smoother. I still have a small surging/rough idle when warm. So, I went ahead and ordered 2 new AC/Delco 02 Sensors. I'm hoping this will fix that. Other than that she seems to be running rather well now. I went ahead and did the fuel filter and pcv valve for extra insurance...although neither had no real effect.

 

Surging can be from a bad/dirty MAF. You can simply try cleaning it or check it's response with a multimeter that shows frequency. If the frequency does not go above 7KHz when you snap the throttle, it's defective.

 

Ok, I believe I have this figured out. I cleaned the MAF tonight. I knew the problem was more of a miss at idle when the car was heat soaked. I was saying surging because you could watch the RPMs go up and down but that was really only by 50rpm or so.

To make a long story short, I read that if you unplug the O2 sensors and force it into open loop....thats one way to check and see if they are causing a problem. So, I did this and it did not help.

I then decided to have a good look over everything while the car was running and doing its thing. I noticed the coil wire was lighting up blueish. So, I replaced it (I have a set of MSD wires that I need to install). This did not seem to help and with further investigation I still notice a faint spark or arc coming from my coil.

So, my coil is bad and this seems to explain why it would miss like this only when the car is heat soaked and in open or closed loop.

 

Those plug wires are a pain to do....Had to even loosen the power steering pump to do them. Also took off alternator and part of the exhaust.

 

Well, I may be wrong once again. After further looking, I can see at least one of my wires on the driver's side arcing along with the coil itself. Man, at least I already bought the wires....just wasn't looking forward to changing them.

An Update. It seems after replacing that bad coil wire first....I have worsened the miss at idle. It now has a stutter until ~2K rpm. I got the driver's side wires on (WHAT A BITCH)! Its not that they are that hard to replace, its all the stupid ****ing clips and **** you have to remove.

Its 4:30am, so I'll do the passenger's side wires this afternoon. As I can see them arcing around the P/S pump. If you look closely its like fireworks.

 

Although it is a bitch to change them, it is not hard just painstakingly slow and your hands will look like you had a fight with a pit bull.

Perry

 

Yeh, the plugs weren't so bad, but the wires were a pita. I took off my starter and alternator when I did plugs. I think it took me as long to route the wires so they didn't touch anything than it did to actually change the plugs.