Thread: new components/ screwy idle

Hi,

My car was running fine but I was concerned about overwhelming the stock MAF and injectors so I decided to upgrade to a bored MAF, 4bar, JWT computer tuned for that combo.

Everything runs fine with the new setup except that it idles like ****. Very rough, shakes the car, and will stall under cold starting. Above 1500rpm it runs great, under boost it runs great, around town it runs great.

I know everyones first impression will be vacuum leak, but it idles fine with the old setup. When I reinstall the old setup and it idles fine again.

I thought perhaps the MAF sensor I purchased is bad so I swapped my old MAF sensor onto the bored housing and it still idles rough.

I thought maybe the adjustable fpr was bad so I tried the adjustable fpr with the old maf at stock fuel pressure. It runs fine.

It seems odd that the computer would be bad since it runs like a champ at basically every point but idle. An interesting side note, when my old setup idles it reads about 16 vacuum on my boost gauge. With the new setup it reads about 10 vacuum. None of the vacuum lines change between setups though so I don't know how I would be getting a vacuum leak. All I am swapping is the MAF housing, fuel pressure regulator, and ECU.

Unfortunately, I do not have a wideband to see if I am rich or lean at idle. I do have datascan however and can log my sensors. Does anyone have any suggestions??? Thanks

its the ecu. I usually use nissan data scan to clear out the saved valves for the tps and force it to relearn. this always corrects the problem.

So use the "clear self learn button" and let it figure things out. How long does it usually take?

Not very long at all, actually. On older cars like ours, the idle relearn is almost instant.

Cool, hopefully that does the trick. I will find out after work today.

also make sure the tps voltage is .45-.48volts with the throttle closed.

Agreed with Mike ^^^

TPS voltage throws EVERYTHING out of whack. Mine is still set to .65vdc when closed, only because the Q45 TPS sits underneath IIRC, and not towards the firewall. I'm just too lazy to correct it, and I'm betting the car will run better with it fixed, but meh.

^^^^^^dude fix yo tps. It messes every thing up.

I'm just too damn lazy to do it, tbh. I'll take a look at it on Friday when I drop the trans to fix the sheared bolt issue.

TPS was already set to .5V, cleared memory, played with idle adjustment screw... no fix. Still idles like ****, still stalls at cold idle. FPR works fine with both setups so I have narrowed it down to bored MAF housing and ECU.

Could the fact that I have cams play a role? Perhaps my old ECU is programmed for aftermarket cams but my new one isnt. Any thoughts?