[RESOLVED] Jerking Problem

[TeeWX98GST]

I have just installed new injector insulators and o rings. Afterwords i tested and had NO boost leaks. Prior to this my boost gauge VAC use to say around -15 (and before the leak started itd sit at -20).. now it idles at 2,000RPM and sits at -20.. but when it drops below that idle (surges a bit) itll vac up to -15.. but I have no boost leaks. AT WOT the car runs amazing with no jerking whatsoever. But anytime I try and cruise at a steady speed, It will jerk pretty bad like I'm not giving it enough gas.. but anytime under acceleration or if the clutch is out it will NOT jerk. I don't really understand what exactly is going on. But to start here's what I know is working. If this helps at all, It killed on me once and when I went to start it it like grinded for a bit before it started up..

Injectors put back in right order - Yes
Boost Leaks - None
Spark Plugs Wires in right order - Yes

So whats going on? Thanks

 

[kenamond]

Are you positive that you reconnected any vaccuum lines and connectors/plugs when you reinstalled the fuel rail? Nothing's jumping out at me, but starting with what you changed is probably a good idea. Double check that you didn't forget to reconnect something.

Are you getting a CEL? If so, get it read; it often tells you exactly what's wrong or gives a valuable clue as to the problem.

If you disconnected the battery for this (I hope you did, as fuel+spark=fire), the ECU was reset, and it might need to recalibrate itself for idle. I recall that you're supposed to let the car idle for 10 minutes after it warms up. Still might take a couple of days for it to find its "happy place". I've never noticed any change in idle when I reset my ECU, but that seems to vary from car to car.

At cruise, the ECU is in closed-loop mode, and at WOT it goes to open-loop mode. I'm not the guru on this, but since you're not having problems accelerating but are having problems at cruise, it might be related to closed-loop mode. Maybe someone who knows more will chime in.

You now have an excuse to buy a logger. That would let you monitor several things that might illuminate the issue a bit.

 

[eagle_talon90]

At cruise, the ECU is in closed-loop mode, and at WOT it goes to open-loop mode. I'm not the guru on this, but since you're not having problems accelerating but are having problems at cruise, it might be related to closed-loop mode. Maybe someone who knows more will chime in.

Could it maybe be something to do with the throttle position sensor at all? When at WOT and the ecu in open-loop mode, its just dumping fuel into the engine, right? And when cruising and the ecu in closed loop mode if the TPS isnt sending the ecu any signals or anything could it maybe still be thinking its in open loop mode causing high idle and all that? Just a thought, I may be completely wrong with what i said so could someone else pitch in on this?

 

[TeeWX98GST]

Could it maybe be something to do with the throttle position sensor at all? When at WOT and the ecu in open-loop mode, its just dumping fuel into the engine, right? And when cruising and the ecu in closed loop mode if the TPS isnt sending the ecu any signals or anything could it maybe still be thinking its in open loop mode causing high idle and all that? Just a thought, I may be completely wrong with what i said so could someone else pitch in on this?

And the solution to my problem... When I lifted up the rail I must have accidently slightly unplugged the throttle position sensor.. I snapped it all the way into place and started my car up and I had an idle of around 900 and a super smooth cruising and WOT

 

[dSmgs-T]

nice haha

 

[eagle_talon90]

Haha, glad to hear you got it fixed!

 

[kenamond]

Could it maybe be something to do with the throttle position sensor at all? When at WOT and the ecu in open-loop mode, its just dumping fuel into the engine, right? And when cruising and the ecu in closed loop mode if the TPS isnt sending the ecu any signals or anything could it maybe still be thinking its in open loop mode causing high idle and all that? Just a thought, I may be completely wrong with what i said so could someone else pitch in on this?

I wasn't sure exactly how the ECU uses the TPS, but I was wondering if something related to it was involved since it's right next to the rail. If the connector was off, I would hope the ECU would throw a code, though.

 

[gsxeclipse97]

what do the two sensor on the TB do? well more so the one of the bottom with the big square plug. I was going over my car today and found that the shop didn't plug it back in.

 

[snowborder714]

The sensor towards the head is the TPS (throttle position sensor) and the one on the bottom of the throttle body closest to the firewall is the ISC (idle speed controller).

 

[kenamond]

And then there's the manifold differential pressure (MDP) sensor smack-dab on the top of the IM. It's only for the EGR system.