Engine stumbles at idle

[Joe 1320]

Chasing this condition, can't seem to figure it out. There is a stumble that lasts only a split second, every 8-9 seconds (like clockwork) only when the engine is not under load. If the car is stationary and in gear, it's perfect. Under 99% of the driving conditions, it's perfect. Runs like a bear, doesn't misfire at any other time. The only time it stumbles is when idling though a parking lot in gear (basically almost no load) or when stationary out of gear (no load against the motor) . It resembles a momentary ignition or fuel cut and immediatly clears out and runs fine. I don't have a scanner like TurboLink where I can capture data, I know that's probably going to be the next purchase......but in the meantime, any ideas? It's been going on for a while, now it's starting to annoy me.
Combo:
motor built by Don Cruz, 109 block, ported irons, ATR billet roller, Lucas #40, Jay Lubrant chip, Walbro, casper's hotwire, headers with no leaks, Ported elbow, 3" kirban Downpipe, no cat, 3" single shot.

 

[getdowngranny]

Scanmaster numbers would really help but since you dont have one we have to look at the basics. Any vacuum leaks? What is your fuel pressure set at?What ignition are you running and is the coil pack and module good to go? Any loose wires? Start eliminating those things along with tapping on the MAF with the car running and also move wires, hoses, and plugs with the car running to see if you can duplicate the symptoms.

 

[kidglok]

Sounds like the fans kicking on killing the car for a sec

 

[Joe 1320]

never said I didn't have a scanmaster, just no laptop based software that allows extensive frame capturing. What I can say is 02s drop momentarily during the stumble. I even have a bar graph mixture gauge that shows what happens in real time rather than based on digital numbers. Switching rate appears normal, 02s normally stay in the range they should, it's just that stupid stumble ever 8-9 seconds like clockwork when out of gear. I can put it in gear and lock the e-brake and it will idle perfectly until it drains the tank. No load and 8-9 second interval must be significant.

 

[turbonut85]

Check your grounds and ohm your battery cables.

 

[dennisL]

There is nothing in your Lubrant chip that runs on a 8-9 sec cycle while in P/N. Just wanted you to know so you could rule out the chip as being the problem.

 

[Joe 1320]

There is nothing in your Lubrant chip that runs on a 8-9 sec cycle while in P/N. Just wanted you to know so you could rule out the chip as being the problem.

That's helpful, it was a concern.

Had the beastie out around town the last few days. I forgot how much difference cool air makes.

 

[whitehot1]

Can you post your scanmaster numbers? Not saying this is your problem but I would suggest getting a more modern chip, something like the TurboTweak chip alot of people running it with great results and it has some features that can be adjusted from what i've read.

I had my car out last night in the cool low 40's air but didn't really notice any difference in the way the car runs when i had it out during the 90 temp. summer nights. Nothing like driving an old turbo regal when it's running right.