Lima 2.5 Idle issues

[DonDumas]

Hi all,
first it has a performance cam, ported intake, ported exhaust, and ported head, cold air intake, aluminum flywheel and a new fuel pump. was running good and progressively getting worse.
It's a 2000 2.5 4 cylinder manual trans with Idle and throttle issues.
while coasting to a traffic light the idle can jump to 3k rpm. surges up and down. after coming to a complete stop the idle will drop down still surges a little but ok. when leaving the traffic light and shifting to another gear the rpm will jump up 500 to 1k in rpm.
I disconnected the idle control motor and connected an old one and left it laying under the hood. Idle still surges to 3k rpm. no vacuum leaks detected only thing I have noticed it ignition advance surging from -1 to 17 degrees?
cam position sensor intermittent?
Anyone seen this before?

 

[Mark_88]

Yes, I've seen it on older engines that had a MAP sensor. Almost exact same symptoms except there were sometimes wild fluctuations in the idle.

Your truck does not have the MAP obviously but I just read where there may be something up with the DPFE if you have one of those. That is on the EGR on earlier models but not sure about your 2000. I had one on my 1996 2.3 that was actually a 2.5 but using the older FI system.

Did you check for codes or do you have the CEL lit up? That's probably the best place to start.

 

[DonDumas]

Hi mark_88,
yes I did check for codes and right now none. But for the last 6 months 171 lean bank 1 and high idle 1506 I think. lean was fixed by fuel pump, high idle fixed by replacing a sticking AIC motor/valve.
just found throttle position at 19.2% just replaced TPS and modified it for .5 volt at idle position. now reads 9%at idle.
just test drove it again with AIC hooked up still have random high idle and timing advance surging. prepped for another test drive with dummy aic hooked up and mounted AIC closed.
Most likely it needs a cpu tune but want to make sure everything is good before I go that way.

 

[tomw]

Could the bellows length of the air tube feeding the engine have cracks that are unseen until the engine torque moves & stretches it? That would allow unmetered air into the engine. Do you have power brakes? A faulty diaphragm could allow air.
Perhaps plugging all the vacuum feeds would eliminate 'hidden' leakers.

For the idle to be increased, you must have air flow. Ain't no way around that I am aware of.

tom

 

[DonDumas]

found about 20 vacuum leaks
the rubber connector for plastic vacuum lines suck they split with in 2 weeks from purchase

 

[Mark_88]

Thanks for the update...vacuum leaks are a PITA to find sometimes but so rewarding when you do find them...