91zxtt

OK, I'm a bit confused and frustrated with this latest issue. I have 2 problems and they're likely related.

The 1st is this....it doesn't matter what gear I'm in....while cruising at any normal speed and applying just enough throttle pressure to maintain a constant speed, the car will buck/jerk/surge (pick your word)...sometimes it feels minor and other times it feels like I'm going to snap something in the drivetrain.

The 2nd is this.....while under hard acceleration...at approximately 3500-4500 RPM's it'll start to stumble or miss. If I gradually increase the RPM's, then it won't do it, but if I stomp on it, then I have issues. Again, it doesn't matter what gear I'm in.

I've adjusted the boost controller each way...I've upped and dropped the boost, increased and decreased the sensitivity, increased and decreased the start boost setting and every combination in between. There are no fault codes.

Most of you know the work that I've done on it. I know we have some very knowledgeable new members, so for those of you don't know about the work I've done, read here...
https://www.zdriver.com/forum/showth...hlight=updates

Thanks guys.

b300z

is it lie where if you just a little bit off the throttle it would jerk or give it a little gas after that and it would jerk again...mine does that. id like to know what it is cuz its annoying

emo236

The later problem you discussed could be an issue of your car running too rich. Does your car run really rich at all? It could also be hesitation...here's the common link I always link to:
http://twinturbo.net/ttnetfaq/FAQpages/hesitate.html
and:
http://twinturbo.net/ttnetfaq/FAQpages/hesitate2.html
I'd say go throught taht list and try everything...see if anything works.

CanyonCarver

I'm sure you double and triple checked ALL of your hose / tube connections, but it sounds like a boost / vacuum leak.

RodMoyes

I know this is going to sound like a stupid question, but I have experienced these same symptoms in the past (with my turbo car)... When's the last time you changed the fuel filter?

Like I said, I know it sounds stupid, but it's the overlooked simple things that always bite the hardest and I didn't see it as a recent fix in the other thread this one linked to.

When I had that issue, I racked my brains (and all the techs that worked for me) and spent a good chunk replacing un-needed parts before putting in an $8.00 Fuel filter and fixing the problem.

Just a thought. If anyone thinks I'm an idiot for asking... Just remember that in my case it fixed the problem so I had to ask. That may not be the problem at all.

Rod.

CanyonCarver

I'll attest to the old saying that one bad tank of gas can clog a fuel filter. Two weeks after brand new filter install, started having problems. It took me another two weeks before I decided to put another new filter in, which solved the problem.

91zxtt

I need to speak with Robert at Z1. They sent me the wrong ecu originally. When they finally sent me the right one it was defective. I wonder if it is the ecu and it's an issue with it running too rich. The stumble at constant speed could just be fouled plugs from running too rich; which could explain why it stends to stumble a little at idle after I've driven it for a while.

The fuel filter is new, but yes I agree, 1 bad tank can ruin it.

I was thinking maybe O2 sensors, but those are new also.

I was also thinking possible MAF, but it's another one of those things....it worked fine before, why would it mess up now.

Final thought,...clogged IACV, but I cleaned it out real well when I had it all apart. Maybe it's just a messed up IACV.

Oh well, it's time;....which I don't have. I have a honey-do list a mile long that I need to work on. I'll get to it all eventually. If you guys think of anything else, let me know.

emo236

good luck on tracking it down and I hope you find your bug. Let us know what it turns out to be.

CanyonCarver

IACV controls idle. It could a problrm, maybe if the valve was stuck open.

I did help another guy out with a somewhat similar problem. Car wasn't running right after new injector install. At idle it would idle fine for about 30 seconds. Then it would start to stumble and miss and then go back to idling fine. My Blazt program showed it was going rich on the left side. When driving, it would start stumbling and popping really bad but would clear up over 3k rpm.

It ended up being, when he put his new injectors in, he damaged / cut a couple of the o'rings causing it to run rich. A heavy coat of Vaseline works well on the o'rings when installing them.

Have you done a boost leak check?