Wandering idle

[thewumpus99]

I've got a Typhoon with a newly rebuilt engine which, when I start it, it idles okay for a minute or two, and then it starts to get rough even without me giving it any gas. The AFR gauge starts ping-ponging between lean and rich, until finally it swings so far into rich territority that the engine stalls completely.

Parts that I think got replaced in the rebuild:
TPS sensor
Battery cable
O2 sensors
Spark plugs & cables
MAP sensor

I took a data log while this was happening using TunerPro:
.ADL file: https://docs.google.com/file/d/0B0w-JDdb37U2NUlFYlF6cFE1MHc/edit?usp=sharing
.CSV file: https://docs.google.com/file/d/0B0w-JDdb37U2dzlrVDhJMU5ybkk/edit?usp=sharing

Any ideas on what to try?

 

[Couger1968]

Re: Wandering idle

I have had basically the same problem for the last 12 years. I tied several things from sensors, Iac valves, vac lines, and ignition. It got a little better. Mine will start and idle fine, then after a min or so will hunt a little and almost stall. Then after that it runs fine. That was even with a 100% stock truck.

 

[milky 1704]

Re: Wandering idle

sounds like you need to get them to someone who can tune your truck it sounds typical of these

 

[thewumpus99]

Re: Wandering idle

It was working fine before with this same computer code and same engine configuration, not really sure what caused this problem to emerge. Now I can't even drive it, sometimes it stalls out even when I'm just slowing down.

 

[Mobile22]

Re: Wandering idle

Someone correct me if I'm wrong but when you're at a cold start your A/F is running off your O2 sensor only. After a minute or so the ECM switches over to your MAP sensor and it can idle really bad until the heads heat up. I've bought a new MAP sensor that was bad once. Start there.

 

[tunerpike]

Re: Wandering idle

Someone correct me if I'm wrong but when you're at a cold start your A/F is running off your O2 sensor only. After a minute or so the ECM switches over to your MAP sensor and it can idle really bad until the heads heat up. I've bought a new MAP sensor that was bad once. Start there.

O2 sensor only comes into the equation once it is heated up. OP needs Tunerpro or Datamaster.

 

[dgoodhue]

Re: Wandering idle

The narrow band o2 sensor should be swinging from rich to lean in closed loop operation. It's pretty normal to have intermittent stumble or miss on SyTy. If the idle is surging is more likely a dirty IAC/passages.

 

[thewumpus99]

Re: Wandering idle

Using TunerPro R/T. AFR input is coming into the computer from a wideband sensor, not the original narrowband. Not surging at idle, so much as that it starts out fine, but then gets lean for awhile, then overcompensates by going way too, then overcompensates by going way too lean, then way too rich, until it finally croaks. Definitely out of whack when driving too (stalls when decelerating, etc.), I just did the data log on it sitting idle because it eliminated a lot of variables.

 

[STOUT74]

Re: Wandering idle

x2 on the IAC. On your datalog, see if the IAC value is fluctuating when it's stumbling.

 

[thewumpus99]

Re: Wandering idle

Mobile22, is there any way to test to see if my MAP sensor is working? Or do I just need to throw in a new one and see if it works?

STOUT74, IAC looks like it starts to wander around, particularly at time 99 of the .CSV file in my original post. It's stable around 34-35, but then it climbs all the way up to 46 and keeps moving around. Pardon my ignorance, but what is IAC?

Thanks guys!

 

[Jkanser]

Re: Wandering idle

Idle Air Controller.

 

[thewumpus99]

Re: Wandering idle

For the benefit of posterity, here is the solution to the problem:

I noticed that the AFR swings always started out in the direction of lean. I hooked up a fuel pressure gauge to the rail, and the psi didn't change even during the lean stumbling, so this seemed to rule out the fuel pump and filter.

1. I cranked the fuel pressure up from 42 psi to 46 psi (to adjust for the fact that I'm driving at 6,000 feet instead of sea level).
2. Recalibrated the Idle Air Controller by jumpering the top right two ALDL pins
3. Rebooted the ECM by pulling the ECM-B fuse for a few seconds
4. Gave the throttle body valve stop screw (manual idle control) an additional turn clockwise

Idle is now stable, and the car hasn't stalled since while driving. Just for good measure, I will run some fuel injector cleaner through the tank, in case the increased pressure was compensating for a poor spray pattern.

This problem originally cropped up while I was doing emulator tuning. It kind of kills me that I spent spent 2 months fruitlessly trying to debug computer flags and fuel tables. In retrospect, it seems as if the computer was thrashing around trying to unsuccessfully compensate for two things which are set by the turn of an old-fashioned screw. And which presumably were no longer set exactly right after the engine rebuild.