Erratic idle PLUS jerk/hesitation while cruising...
 

Hey guys, I am having this problem on a built motor Greddy TT with Fcon and can't seem to find the problem, oh with Carbonetic twin disc if that matters. At idle, it jumps around 800 to 1100 up and down. And then at cruising speeds, if I barely give it gas it jerks and hesitates. Any ideas??? If I keep the cruising speeds below 2k its fine. So when I cruise now, I keep it in a higher gear so that it doesnt jerk. But if I give it a little more gas, the car is fine and runs fine...

What cams do you have? Has your ECU been re-flashed?

What is your air/fuel ration at cruise and idle, and who tuned it?

it could be one or more of many things

- bad inputs in the fuel or timing map
- bad throttle settings
- bad fuel cut settings or maps

basically I would take it to an Fcon tuner and have it checked out.

Has it always done this, or did it just start? Has the car been tuned?

It was actually just tuned like a week or so ago. It has GTM turbo stage 1 cams. At idle, the afr's read in like the 20's :( And cruising speeds with very light throttle it will read between 17-20's :( DEFINITELY LEAN. And yes this problem just started. It actually started up like a day or two before the tune, but after the tune it was ok. Then about a week or week and a half it started doing it again and seems worse...

Ideas?

check your fuel pressure....if that's good research the laws in your state regarding battery.

I was going to say the same thing, have the fuel pressure checked out.

if is erratic like that it could be the fuel pressure as mentioned but also check other sensors like the boost and temp sensors used for the Fcon, I had an issue with the boost sensor and just caused the air fuel to be all over the place

Just an idea, but is one of your banks of injectors going lean? I have a FCON and the dual wideband AFK and sometimes after the 2000 rpm range if I am just cruising one side of the engine will run lean for a second and the car sputters. If I blip the gas for a second it goes away. I only notice this when I am cruising and barely touching the gas pedal. Under boost and WOT everything is ok.

Check the MAF too, as well as fuel preasure

As in boost sensor not hooked up? Or broken? And the only other one is the intake temp sensor, right?

yes, boost sensor started to act up and was reading 1 psi off at time which would put the Fcon in cells for the wrong boost.

The temp sensor should not go bad, but if did the effect would be the same all the time

I was pming a guy with similar problems, and GTM believes it was his O2 sensor. He had JWT TT and FCON. But then again he already knew his sensor was toast.

My money is on some kind of sensor problem.

i had exactly the same problem before. It was a flywheel speed sensor they forgot to plug back in when they installed my clutch. Make sure you get your car checked asap. Most likely it's something mechanical. My car also had exactly same symptoms and it had a greddy TT as well. I went back to the tuner and he couldnt figure it out, even reset the tune back to stock and it still would idle up and down and behave weirdly in boost and make unusual sounds.

Awesome i appreciate it guys. Figured out my sensor was going bad :( But anyway, got another one. I have no oil pressure at start up. It probably takes like 2-3 seconds and then it builds oil pressure... Any ideas? I replaced the oil pressure sensor and I do my best to do my oil change about every 2.5k miles. I currently run 300V 15w-50.

15w-50. isnt that way to high of a viscosity for a turbo'd motor? might be the motor taking a while to get the oil at a good operating temp.

then again, with thicker oil you would have more resistance to flow. which means higher pressure readings.

:+1: 15w-50???

I've got this same issue...I'm HKS FCon + GReddy TT...I actually have O2 sensor faults...6 of them. Now I highly doubt all my O2 sensors are failed...possibly the fault was set once upon a time and is still causing issues? I need to get the fault cleared and see if it comes back...but this weekend I'll take a look and see if I find any other things wrong.

Basically, under heavy throttle I have no issues at all, but idle sometimes bounces up and down, and while cruising with barely any throttle I'll get random hesitations.

Also, my wideband reads AFRs in the mid 14s while cruising, 12s in boost, so I'm pretty sure I'm fine on that.

Has anyone found a for sure cause of this?