idles high intermittent 3k rpm, lean at 1k rpm

[MotorHead265]

I have looked threw all the threads and I cant find anything related. My car will being idling fine and il start driving and or sitting still and it will rev up anywhere between 1500 to 4000 rpm and hold. It causes problems at red lights and. Il tap the gas and it wont really do much. I have checked all my intercooler piping and its all tight. Also at idle when it does idle right the afr is around 16.9 to 17ish. I know this is not good. Im not sure what else to look at. all help is greatly appreciated.





Garrett T04S 60-1 70mm turbo Megan Racing O2 Housing Greddy type-s bov 24x12x3 inch Greddy intercooler 3 inch custom intercooler piping 255l/hr walbro fuel pump Apexi N1 3 inch catback....no cat Apexi N1 3 inch downpipe K&N cone filter

Engine Management:
maf translator and stock ecu

Engine Internals:
93 port and polished head intake and evo 3 mani 91 block eagle rods ross pistons 0.040 over bananced and polished crank Clevite-77 main and rod bearings Balance shafts removed ARP rod bolts, main cap bolts and head studs 3g lifters Cometic head gasket Mitsubishi timing belt
Drivetrain Modifications:
stock rear stock trasfercase modified evo 3 trans stock axels ACT 2900lb. clutch

Suspension Modifications:
Tien lowering springs Tokico adjustable shocks Prothane upper and lower control arm bushings Prothane Motor and transmission mount bushings

 

[Ronnienormand]

Technically speaking, it could be hundreds of things. More commonly, you could suspect things like: broken vacuum hose (or intake leak before mass airflow sensor), faulty or malfunctioning sensor (idle-air control, intake air temperature, etc...)


The engine idles too fast. After the engine has run long enough to be warm, the idle speed does not come down to normal. You really notice it when you come to a stop and must have to push hard on the brake pedal to keep the car from moving.

Possible causes:

1.If you have a carburetor, you may have a bad accelerator pump or power circuit.
The Fix: Replace accelerator pump or replace carburetor.
2.The engine may be overheating.
The Fix: Check and repair cooling system.
3.The fuel pressure regulator may be operating at too low a pressure.
The Fix: Check fuel pressure with a fuel pressure gauge. Replace fuel pressure regulator. (Generally not a DIY job)
4.The ignition timing may be set wrong.
The Fix: Adjust ignition timing.
5.There may be some type of ignition problem.
The Fix: Check and replace distributor cap, rotor, ignition wires and spark plugs.
6.There may be a fault in the computerized engine control system.
The Fix: Check engine control systems with a scan tool. Test circuits and repair or replace components as required. (Generally not a DIY job)
7. There may be a vacuum leak.
The Fix: Check and replace vacuum lines as required.
8.You have a bad idle speed control unit.
The Fix: Replace idle speed control unit.
9.The alternator may not be working properly.
The Fix: Replace alternator.


Please let me know if you find anything out.

 

[MotorHead265]

I have checked just about every sensor and everything looks ok. I am also having an intermittent miss for a sec to 5 secs then goes away. the idle isnt idling as high usually around 1000-1500rpm now. Its still running lean on idle

 

[Absit]

Have you been through Terry's Talon Troubleshooting Guide?
Are you reading off a wideband?

 

[MotorHead265]

So I put a smoker laek detector test on it and found a leak in the intake gasket but i noticed now that it looks like oil on the tops of the pistons ands im losing oil. The motor is supposed to have around 10,000 miles on it compression is 165 150 145 150.

 

[bertrenolds]

Fix your boost leak at the intake manifold and then do a leakdown test to see if your valve seals are bad. What part of the motor? The bottom could have 10,000 miles but they threw a used head on it and the valve seals were bad, who knows.

 

[Bouche Dag]

Bad ISC? Sticking FIAV? I would also go through Terry's Troubleshooting guide.