Open Loop Symptoms?

[BpuVR4]

this is an idle question, but split up into a couple different ones. I am waiting on my Keyspan serial to usb adapter to come in to hook up data logger. keep in mind my car runs pretty well...driveability not a factor here. just trying to iron out this issue.

symptoms:

1. most of the time, car idles well...stays around 900rpm. car will warm up at 2k rpm, and will come down to 900~ after its warmed up. However, there are times, the idle will keep at 2k, esp after a highway run. Eventually, if I drive the car long enough, it'll come down to 900, then slowly surge up to between 1100-1500 and come back down to 900, then repeat.

2. 75% of the time, the car runs well...the motor feels solid, boosts well. however the other 25% of the time, I can feel the motor becoming butter smooth..a bit quieter and seems like flat out runs better. idles well most of the time.

3. when I adjust the idle by grounding the connectors, it'll idle rock steady, then when I disconnect the grounds, it'll idle a little more erratically.

my big suspicion is the ect sensor. I tried to replace it last week to give it a shot, but received the wrong one. I was gonna wait to hook up the data logger to see what it tells me but waiting on the Keyspan adapter is taking awhile. I also do not have a multimeter here with me.

I'm wondering if symptom #2 is telling me that most of the time, my car is not reading fully closed loop? anyone else experience this? ISC's been replaced in Sept, intercooler piping t-bands get tightened/checked once every couple weeks. I'm getting right about 20mpg or so.

 

[Gmoney1983]

I'll be watching this. Curious to see what you find out as I've been fighting a very similar problem. Although on mine if I pop the throttle it will settle right back down to a decent idle speed.

 

[BpuVR4]

i try that...a couple cars ago I had an MR2 which are known for air bubbles in cooling system (doesn't seem as relevant to VR4's). Sometimes when it's warmed up- or so I assume...sometimes when I jack the heater up to high itll come down and then surge slowly. Guys on this forum are way smarter than me, and I like to do my research/check hunches before I start digging.

 

[ktmrider]

464 had very similar issues when I picked it up.

Ultimately it was ECU related, one or more of the ISC drivers was bad likely due to using a bad ISC motor. Found it by swapping ECU with a known good DSM one.

Reminder, the ECU feeding info to ISC position controls idle at all levels including cold start ( ECU coolant temp sensor is primary with FIAV adding extra air to aid ISC ). My ISC was only reading 47ohms on one coil, other three were in spec at 30ohms. That small increase in coil resistance knocked out part of the ISC control circuit. Side note, my ECU had been repaired on at least one occasion so it was already a bit fragile.

Good ISC, good ECU, rock solid idle at all levels.

 

[BpuVR4]

i got a non eprom ecu, will give that a go, thanks for the insight KTM

 

[BpuVR4]

swapped ecu's and went for a quick run to the liquor store mile away (x2 cause I dropped the bottle of jack after I got it home). initial warmup had it warming up at 1300rpm instead of 2k. drove her after it was warmed up....any surge that happeneded ending with the motor calming back down sooner than w the Eprom ecu, although there were bouts of it staying at 2k for a while, but still calmed down. Gonna drive her w the 2nd ecu for now, recheck the t-bands on the piping and see how it goes until further advice or get the data logger running.

 

[BpuVR4]

been driving on the different ecu last few days. overall quality may be a little better, however I still see bouts of 2k rpm about 35%-40% of the time. when the idle slowly rises up, I've noticed on my SAFC that the correction value goes up, but the throttle % does not- don't know if this indicates anything, but thought I'd note it. when i have access to garage, gonna do some more investigating. really want to set up the logger, but darn the christmas time shipping

 

[G]

SOunds like air in your cooling system. Have you recently done work to it?

 

[rdomeck]

Quoting MoMoVR4:
swapped ecu's and went for a quick run to the liquor store mile away (x2 cause I dropped the bottle of jack after I got it home). initial warmup had it warming up at 1300rpm instead of 2k. drove her after it was warmed up....any surge that happeneded ending with the motor calming back down sooner than w the Eprom ecu, although there were bouts of it staying at 2k for a while, but still calmed down. Gonna drive her w the 2nd ecu for now, recheck the t-bands on the piping and see how it goes until further advice or get the data logger running.



Alcohol abuse man! This is just not right. Glad it wasn't a bottle of Pappy Van Winkles /ubbthreads/images/graemlins/wink.gif

 

[BpuVR4]

Quoting G:
SOunds like air in your cooling system. Have you recently done work to it?



only thing recent was trying to swap the ect sensor to see if that was causing the high idle, but found out late it was the wrong one.