open loop high idle 2.5 dohc

[jim milewski]

in trying to get this to idle at at lower and correct rpm could it be the O2 sensor having a problem preventing it from going into closed loop operation, I read a post saying that open loop will idle high, which means I should not even be looking at the IAC until I resolve the open loop and get it to run in closed loop. I'm not getting an O2 sensor code though, is there anything else that could prevent closed loop operation. I have a new pre cat O2 sensor on the way

[Legacy777]

Are you using a scan tool to determine that the car is still in open loop?

 

Can you give us a little more background on the high idle problem. Is this a recent problem or have you had it for a while? Anything that may have changed when you first started having the problem?

[jim milewski]

thanks Josh, ya, big changes, I pulled the engine, planed the heads, new headgaskets, timing belt, pulley, water pump, seals, clutch. It runs strong and no metalic noises (praise the Lord!), but the idle is high, I replaced the IAC (had codes for it), so will see today if that helps, it was staying in open loop so I replaced the front O2 sensor yesterday as well, so today I will see if there is a change, just have a few vacuum line issues (my other post), I went around with starting fluid spraying for intakes leaks and everything seems tight best I can tell. This is my first Subaru and have heard people say negative things about the 2.5 dohc, but I like this engine, if i get this idle straightened out and the overheating doesn't return I'll be really happy!

[jim milewski]

forgot, yes, using a scan tool, it is OBD.com program for my laptop with that special cable, so it does code reading and dynamic run time monitoring. I think I might have damaged the O2 sensor by having the engine removed, the hood off, the car outside, the uncovered exhaust headers open pointing up drinking in lots of rain water.....pretty stupid..huh

[jim milewski]

I also forgot to say that I did not replace the IAC valve "on a hunch", but rather because I took it off and took the plastic cover off and put a pair of pliers on the soft (very easily breakable, really very easy) ferrite magnet seeing if it lifted out, don't ever try this, leave this section alone and clean down below and apply voltage and test it that way......Ebay for $50

[Legacy777]

Jim,

 

Sounds like you're probably on the right path with the O2 sensor & IAC based on what you described. I guess keep us posted on what you find out and if you still have issues, we can troubleshoot from there.

[Gloyale]

IF the ECU thinks the engine temp is low, it will stay in open. If it can't control idle,(unmetered air leak) it will go open (and on some ECUs cut #1 cyl fuel)

 

Also, there are driving conditons the ECU will go OPDC. OPen for Driving Conditions. Either to accomodate fuel cut for coasting, or full enrichment under WOT.

 

If the VSS is reading a pulse, and the Throttle/idle switch is closed, it will assume the car is coasting, and go open to cut fuel OPDC.

 

Similarly, it will go OPDC for a full throttle. So check out the range on the TPS, and make sure the Idle switch is working correct.

 

 

These are just gusses where to start looking. Just some of the conditions the ECU will go open loop for.

[jim milewski]

thanks Gloyale, I have two coolant sensors, my temp gauge works, is one for the gauge, the other for the ECU? Can a test be done with a voltmeter. All temp sensors I have seen are the thyristor type which changes resistance with temp change. Would you happen to have a wiring diagram for these two sensors so I can access the wires by piercing them at a workable spot and take cold and warm readings to see if the sensor to the ECU is working. Another thing that you pointed out and I want to see if I understand, when the ECU detects a "coast" condition it goes into an open loop mode and cuts fuel as it is not needed? This is very clever!

[jim milewski]

Today I installed the IAC valve I got off ebay because I broke the original, also installed the front O2 sensor because I broke the original (I went with an inexpensive $30 free shipping off Ebay) where you use the connector from the original, I rewired the coil connector so the yellow wire from the main harness mates with the red wire on the coil pigtail and vice versa, I had to rewire because I rewired the first time wrong. The update is my high idle and full time open loop running is fixed, now I'm close loop after warm up and idle is 700 rpm. It all started last fall with a blown head gasket, I went with the newer revised three layer Viton coated Felpro and got the heads resurfaced and new exhaust studs, short test rides and no overheat problems (before I could not go three miles and I was way too hot). Possible power steering problem with an occasional shudder (I put in ATF like the cap said, does it require some sort of bleeding or does it work itself out?), at any rate I'm getting real close to finish, thanks to all the good advice I got here, what a great reserve of knowledge!

[Legacy777]

Good to hear you got it fixed. Any idea which one or possibly a combination of both that actually fixed the problem?

 

As for the ATF, the system will bleed the air out from normal driving. Slowly turning the wheel lock to lock will usually get any air out.