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Cold XT6 Idling Poorly


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7 replies to this topic

#1 Left_coast*9

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Posted 22 March 2005 - 03:04 PM

Hey folks, my 1988 XT6 AWD 5 spd is having some trouble idling when cold. It starts right up, RPMs go up to about 1600 or 1800 just fine. But within 30 seconds or so RPMs drop to ~ 1-200 RPMs, the car glugs there for a few seconds, and the RPMs return to 1800 or so. This cycle continues up and down or until I drive the car away. Once underway, the throttle sticks at about 3000 RPMs with normal driving, then drops down again in 5-10 seconds to normal level if I stay out of gear and off the throttle. Runs fine while I'm actually driving. Wierd.
When the car is warm, it idles fine at about 750 RPMs, although a bit rough.

I replaced the "throttle control valve" on this car (located on top of the engine, just behind the intake manifold, passenger side) with a used unit, but it didn't solve my problem. Made it worse, actually. Just my luck.

Any thoughts? Does this sounds like a throttle control valve issue? Do I have a vacuum leak perhaps? Is there some sort of choke assembly I can check or replace? H E L P, P L E A S E ! thanks all...

#2 grossgary

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Posted 22 March 2005 - 09:17 PM

WOO HOO!!
XT6 questions.

has your check engine light ever come on?

a couple things could be your problems:

do a complete tune up. particularly the spark plugs (use the stock NGK, they are great plugs), distributor cap, rotor and wires. you can try neglecting the wires if you need to save cash, otherwise i say replace them and i highly recommend magnecor wires if you plan on keeping the car for awhile.

now that your ignition is golden - clean your IAC valve. Idle Air Control Valve. two 10 mm bolts and a bracket hold it to the intake manifold with a hose going in both sides of it. don't bother replacing it. remove it and keep spraying electrical contact cleaner or brake cleaner (any cleaner that doesn't leave a residue), keep cleaning until no more black dust comes out.

now the water temperature sensor. i would suspect this is the cause of your irratic idle problems. but your check engine light should come on (but not necessarily - have seen coolant temp sensors cause problems without triggering the CE light, but no usually). next to your thermostat and the second coolant cap (not the one on the radiator) is an electrical sensor, that's your water temp sensor that will cause problems. these little annoyances cause problems ALL THE TIME. i've owned 7 XT6's and of the ones that i've driven for any length of time i've had numerous run ins with this coolant sensor. don't replace the sensor. the electrical contacts will be the problem. if you wiggle this connector while the car is idling you might hear the engine jump all over the place, stall or smooth out to a perfect idle as you wiggle the connector around. this is one way to verify this thing is causing you problems. even if you don't experience this, check the connectors. remove the harness and typically you'll see green corossion. i actually did a permanent fix to this reoccuring issue. i finally cut the wiring harness off and cracked one side of the plastic on top the sensor (just for added room/space) then soldered the wires directly to the sensor contacts and used some shrink wrap to cover them up. then i spliced in connectors a few inches away on the wires so i can remove the water temp sensor if i need to. i posted a picture of this mod here:

http://www.ultimates...ead.php?t=27923

if you plan on keeping the car this is a great mod to do, it's very easy and saves you lots of headaches and annoying surges and inconsitent performance in the future.

another option for your idling is the MAF sensor. i would expect some noticeable drivability problems though, not just at idle. an easy way to inspect the MAF is to remove it and look internally under good light. you'll see very very fine wire (hot wire anemometer type device) inside the MAF sensor. these wires can snap/break. they are extremely thin so have good light around to inspect them. a broken wire will cause terrible driving and gas mileage. this does not gaurantee your MAF is good, but may show if it is bad. swapping in a known good unit is a great option.

if you did everything above i would be very surprised if the car didn't run much better. but if not we'll explore other options. compression test all cylinders, bad gas, bad air filter...could also be problems. but i would do a tune up as suggested above, clean the IAC and then check the MAF and water temp sensor. this can all be done yourself easily and doesn't take that long and doesn't cost much and makes me write run on sentences.

good luck.

#3 Left_coast*9

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Posted 23 March 2005 - 03:32 PM

Gary, you're a STAR! Thanks a ton for the response. I actually just recently completed a full tune-up (including wires) on this vehicle, among other things like a new clutch, engine seal, alt., oil pump, water pump, serp. belt, etc. You could say that I'd like to keep the car. These XT6s are awesome, esp. w/a 5 spd! The tune up really helped the drivability. Now it's just this pesky idling problem. I will clean the original IAC valve, and check into the coolant temp. sensor issue and then report back. **fingers crossed**
Blake

WOO HOO!!
XT6 questions.

has your check engine light ever come on?

a couple things could be your problems:

do a complete tune up. particularly the spark plugs (use the stock NGK, they are great plugs), distributor cap, rotor and wires. you can try neglecting the wires if you need to save cash, otherwise i say replace them and i highly recommend magnecor wires if you plan on keeping the car for awhile.

now that your ignition is golden - clean your IAC valve. Idle Air Control Valve. two 10 mm bolts and a bracket hold it to the intake manifold with a hose going in both sides of it. don't bother replacing it. remove it and keep spraying electrical contact cleaner or brake cleaner (any cleaner that doesn't leave a residue), keep cleaning until no more black dust comes out.

now the water temperature sensor. i would suspect this is the cause of your irratic idle problems. but your check engine light should come on (but not necessarily - have seen coolant temp sensors cause problems without triggering the CE light, but no usually). next to your thermostat and the second coolant cap (not the one on the radiator) is an electrical sensor, that's your water temp sensor that will cause problems. these little annoyances cause problems ALL THE TIME. i've owned 7 XT6's and of the ones that i've driven for any length of time i've had numerous run ins with this coolant sensor. don't replace the sensor. the electrical contacts will be the problem. if you wiggle this connector while the car is idling you might hear the engine jump all over the place, stall or smooth out to a perfect idle as you wiggle the connector around. this is one way to verify this thing is causing you problems. even if you don't experience this, check the connectors. remove the harness and typically you'll see green corossion. i actually did a permanent fix to this reoccuring issue. i finally cut the wiring harness off and cracked one side of the plastic on top the sensor (just for added room/space) then soldered the wires directly to the sensor contacts and used some shrink wrap to cover them up. then i spliced in connectors a few inches away on the wires so i can remove the water temp sensor if i need to. i posted a picture of this mod here:

http://www.ultimates...ead.php?t=27923

if you plan on keeping the car this is a great mod to do, it's very easy and saves you lots of headaches and annoying surges and inconsitent performance in the future.

another option for your idling is the MAF sensor. i would expect some noticeable drivability problems though, not just at idle. an easy way to inspect the MAF is to remove it and look internally under good light. you'll see very very fine wire (hot wire anemometer type device) inside the MAF sensor. these wires can snap/break. they are extremely thin so have good light around to inspect them. a broken wire will cause terrible driving and gas mileage. this does not gaurantee your MAF is good, but may show if it is bad. swapping in a known good unit is a great option.

if you did everything above i would be very surprised if the car didn't run much better. but if not we'll explore other options. compression test all cylinders, bad gas, bad air filter...could also be problems. but i would do a tune up as suggested above, clean the IAC and then check the MAF and water temp sensor. this can all be done yourself easily and doesn't take that long and doesn't cost much and makes me write run on sentences.

good luck.



#4 Left_coast*9

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Posted 23 March 2005 - 04:37 PM

Oh, sorry, no check engine lights have surfaced at all, to answer your question.

Gary, you're a STAR! Thanks a ton for the response. I actually just recently completed a full tune-up (including wires) on this vehicle, among other things like a new clutch, engine seal, alt., oil pump, water pump, serp. belt, etc. You could say that I'd like to keep the car. These XT6s are awesome, esp. w/a 5 spd! The tune up really helped the drivability. Now it's just this pesky idling problem. I will clean the original IAC valve, and check into the coolant temp. sensor issue and then report back. **fingers crossed**
Blake



#5 Left_coast*9

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Posted 24 March 2005 - 11:24 AM

Ok, so I removed and cleaned the IAC valve and no noticable change. But I did inspect the coolant temperature sensor and sure enough, it's green and corroded. I figure I should also solder the connections and replace the wiring back aways, as you suggested.
I did not get into the MAF sensor - figure I should solve this problem first.
I have a couple other questions:

Do you know what gauge the coolant temperature sensor wire is?
What kind of choke does the XT6 have? Is it vacuum controlled? The more I drive and experience/think about the symptoms, the more it seems the real problems are at start-up, in the morning or when the car is cold. It will not idle, just revs up to 16-1800 , then dies as I described. If I drive off, it runs, but the engine sticks at between 3K and 4K RPMs (between shifting, for example, hell it wants to stay there even when in gear) until the car comes to full temp, then it's fine, idles roughly at around 750 RPMs. At ANY time when the car is accelerating, it pulls hard and evenly. FYI

#6 grossgary

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Posted 24 March 2005 - 08:08 PM

i'd go ahead and rewire that coolant temp sensor. don't know gauge, but it's not all that important either. i use heavier than what is on there stock. address this first, if you can solder it's a very easy and one of the best fixes you can do on your XT6. this isn't a chance item, it will eventually cause issues.

now that im' done preaching, address your MAF sensor next. these two items i think are very crucial in your situation. after these two are checked out, i'm not sure where i would go next, but let's cross that bridge when we get there.

i have some ideas but don't want to overload with random ideas yet because your problems are very indicative of water temp sensor or MAF issues.

also - the TPS is very tricky to adjust and the FSM procedures for setting the TPS WILL NOT WORK. they are incorrect. have to set it *by ear* essentially.

on a side note. had an XT6 with no check engine codes that had some erratic RPM issues. couldn't figure out the problem through maintenance items and swapping sensors. i finally realized that if i played with the TPS wires about 8 inches from the sensor the car would stutter, shut off, rev up and just go wild. i spliced in some new wires and the thing ran great. so keep your eye on a short like this when you're looking at the TPS, WTS (water termp sensor and MAF sensors. the wires just prior to these sensors can also experience problems. now i generally move wires around systematically for each sensor in order to get shorts to show themselves.

i've put 350,000 miles or more on XT6's and i've only ever had to replace one sensor. a MAF sensor last year. (not including O2 sensors). every other sensor issues has been corrosion or short related.

good luck and you can email me if you have any questions. my time on this board while generally consistent can vary.

#7 Left_coast*9

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Posted 25 March 2005 - 05:30 PM

Great, thanks again. I WILL be performing that mod on the WTS this weekend, and check some more into the MAF, and report back Monday. Till then...



i'd go ahead and rewire that coolant temp sensor. don't know gauge, but it's not all that important either. i use heavier than what is on there stock. address this first, if you can solder it's a very easy and one of the best fixes you can do on your XT6. this isn't a chance item, it will eventually cause issues.

now that im' done preaching, address your MAF sensor next. these two items i think are very crucial in your situation. after these two are checked out, i'm not sure where i would go next, but let's cross that bridge when we get there.

i have some ideas but don't want to overload with random ideas yet because your problems are very indicative of water temp sensor or MAF issues.

also - the TPS is very tricky to adjust and the FSM procedures for setting the TPS WILL NOT WORK. they are incorrect. have to set it *by ear* essentially.

on a side note. had an XT6 with no check engine codes that had some erratic RPM issues. couldn't figure out the problem through maintenance items and swapping sensors. i finally realized that if i played with the TPS wires about 8 inches from the sensor the car would stutter, shut off, rev up and just go wild. i spliced in some new wires and the thing ran great. so keep your eye on a short like this when you're looking at the TPS, WTS (water termp sensor and MAF sensors. the wires just prior to these sensors can also experience problems. now i generally move wires around systematically for each sensor in order to get shorts to show themselves.

i've put 350,000 miles or more on XT6's and i've only ever had to replace one sensor. a MAF sensor last year. (not including O2 sensors). every other sensor issues has been corrosion or short related.

good luck and you can email me if you have any questions. my time on this board while generally consistent can vary.



#8 Left_coast*9

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Posted 02 May 2005 - 01:18 PM

Well, it's been awile, but just wanted to get back and close the book on my problem, and this thread. Turns out I had a damn leak at the intake manifold. I replaced the gaskets and now it runs like a dream again. When cold, it starts right up and purrs like a kitten at about 11200-1500 RPMs. Drivability at all temps/rpms is also improved. Thanks for your help!

Blake




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