what causes the idle to change?

[zalnn]

my car started idling high today (between 1500 and 1800 rpm) even after the engine reached its normal running temp (little less that halfway up the temp gauge).

so i turned the car off and on and it stabilized after about 30 sec. but 1/2 mile later at the next intersection it was high again.

immediately i though, "shit, iac is on its way to getting focked" so i pulled over and unplugged it; did this so that it wouldn't short out internally and overdrive the ecu and cause damage to the ecu. before unplugging the iac turned the car off then back on the get it to the correct rpm at idle.

again the car was fine for a while, and then it started idling all funny. the idle is not choppy, its a gradual and smooth change. the car doesn't stall either.

my only guesses are the fiav and the biss screw.

do you guys have any input?

[SAgosto]

Soo many things. Timing, leaks, BISS, etc..

[EvilNCarnate]

[quote=""Shawn96VR-4""]Soo many things. Timing, leaks, BISS, etc..[/quote]
I guess we have to say it... Datalog. Good place to start, IAC check, throttle position then start looking for small vac leaks, BISS leak or loose BISS screw... So many options so little time.

[zalnn]

timing?... timing can cause the idle to go up and down?
i am going to check the biss as soon as i find a screwdriver at work.
its an SL, not much to leak, but i will check for that too...

[SAgosto]

Yes, timing alters the idle.

[zalnn]

[quote=""EvilNCarnate""]I guess we have to say it... Datalog. Good place to start, IAC check, throttle position then start looking for small vac leaks, BISS leak or loose BISS screw... So many options so little time.[/quote]

no data logger; its a '94 SL with no mods and therefore didn't have a reason to buy a data logger.

check list
1. biss screw
2. timing
3. tps

[EvilNCarnate]

[quote=""zalnn""]no data logger; its a '94 SL with no mods and therefore didn't have a reason to buy a data logger.

check list
1. biss screw
2. timing
3. tps[/quote]

After that I would pull the IAC and test it out, should be able to find the resistance and pinout on 3si or stealth316. Also check the throttle cable, make sure it has a small amount of slack and moves freely (with the engine off). Without a datalogger figuring things out comes down to individual checks and adjustments. The better you know your health car the better you might be.

[zalnn]

how do i check the crank timing marks?
does the wheel and lower timing belt cover need to come off?

[EvilNCarnate]

[quote=""zalnn""]how do i check the crank timing marks?
does the wheel and lower timing belt cover need to come off?[/quote]

Yeah, covers off for the cams, the crank itself I think you need to remove the dampener to see its mark. I would pull the belt covers up top and see if both cams locations line up correctly. If it jumped timing though it was probably at the crank and thats a lot of work to check. Datalogger would really make it easier.

[moffman93']

the hole in the crank gear should match up with a line on the oil pump.

[niterydr]

Sounds most likely like an intake manifold leak/big intake leak that opens up with heat, therefore bypassing and allowing more air into the engine.

I would start with a leak test.

[zalnn]

[quote=""EvilNCarnate""]Yeah, covers off for the cams, the crank itself I think you need to remove the dampener to see its mark. I would pull the belt covers up top and see if both cams locations line up correctly. If it jumped timing though it was probably at the crank and thats a lot of work to check. Datalogger would really make it easier. [/quote]

dammit... i was hoping that i didn't need to remove the dampener aaarhg! my parking lot situation is less that ideal, given the 33F temps were are going to see for the next few days.

[quote=""niterydr""]Sounds most likely like an intake manifold leak/big intake leak that opens up with heat, therefore bypassing and allowing more air into the engine.

I would start with a leak test.[/quote]

i am going to look for a leak first. seems easier, and should be able to duct-tape that till i can get her home into a garage after new years.

i'll give you guys updates on the 26th, when i get back from christmas.

for now you all have a merry christmas

[EvilNCarnate]

[quote=""moffman93'"]the hole in the crank gear should match up with a line on the oil pump.[/quote] You cant see through the dampener, the holes in it are for the tool used to hold it in place while you remove and install it. The required torque is something like 130ft-lbs (dont quote me on it). The Dampener is removed and then you can see the dimple on the crankshaft pulley and align it with the point on the oil pump.

[quote="zalnn""]dammit... i was hoping that i didn't need to remove the dampener aaarhg! my parking lot situation is less that ideal, given the 33F temps were are going to see for the next few days.



i am going to look for a leak first. seems easier, and should be able to duct-tape that till i can get her home into a garage after new years.

i'll give you guys updates on the 26th, when i get back from christmas.

for now you all have a merry christmas[/quote]
Check that you IAC is plugged in. I remember this 'story' I heard. These two guys were working on a 3000GT well into the next morning. After 11 hours they had her back together and fired her up. The idle sat at 1800rpms. The car ran well on a test drive around the block. The two figured something must be up with the idle as the IAC was brand new along with a dozen other parts. They hooked up the datalogger and saw an odd value for IAC. They then looked and noticed nothing was plugged into the IAC. During re-assembly someone had forgot to plug the IAC back in or the cable had been knocked off. The car still ran perfectly durin a short test drive but the idle was really high. I cant remember where I heard the story but I firmly believe it to be true.

Here is exactly what I would do if this were my car. First check all cables are plugged in. IAC being one big one. Then start looking for leaks, cracked lines, open holes, removed lines etc, tape all inlet location connections to see if idle changes. Check MAS honeycomb for damage. Ground the brown lead to set idle/check timing and get a timing gun and see what the timing is at. Pull IAC and test resistance. Check the cam timing marks. Ground pins 10/11 on ecu and adjust idle down, remove grounds and start car back up. Check idle, check idle with AC on then recheck timing. Last pull shit apart and physically check the timing marks on the crank.

Here are a few links for you. One on timing test, one on IAC/ISC test, one on 60k that will help if you have to go that far down.

http://www.stealth316.com/2-ignition-timing.htm
http://www.stealth316.com/2-isc-iac.htm
http://www.team3s.com/60k.htm

[zalnn]

for anyone else who needs information, in addition to evilcarnate's links here are a one more that i found;
http://www.3si.org/wiki/index.php/Idle_Speed_Adjustment

[zalnn]

It was the IAC, after pulling it apart and cleaning it, the car idled fine.
I found that NAPA sells them for $104 + tax if that helps anyone.

Thanks for all the help guys!

I had left me car in first gear pointing upwards on a slope with the e-brake off; this can cause the timing belt to jump a tooth or so. And coincidently the IAC getting stuck, caused me to be in a state of panic all the way through Christmas; I was at the in-laws faaar away from my car.

[EvilNCarnate]

If you buy one make sure its a Mitsu OEM. Most places sell remaned ones. DSMISC.com sell them for like 130. I bought one since I had the money and its a common problem issue on our cars. I pulled mine and cleaned it one time trying to find my idle issue. Ground Wire kit from bigtyla helped it a bit, then I found the honeycomb in my MAS had come loose and turned sideways. Those helped it for a while until my battery started to go. I didnt know it was going bad until I got up one morning, hit the key and got a few clicks. Took it down and they tested it, wouldnt hold a charge. Got a new battery with a few more amps and she sparked up and idled perfectly again. Glad you got it working.

[zalnn]

[quote=""EvilNCarnate""]If you buy one make sure its a Mitsu OEM. Most places sell remaned ones. DSMISC.com sell them for like 130. I bought one since I had the money and its a common problem issue on our cars. I pulled mine and cleaned it one time trying to find my idle issue. Ground Wire kit from bigtyla helped it a bit, then I found the honeycomb in my MAS had come loose and turned sideways. Those helped it for a while until my battery started to go. I didnt know it was going bad until I got up one morning, hit the key and got a few clicks. Took it down and they tested it, wouldnt hold a charge. Got a new battery with a few more amps and she sparked up and idled perfectly again. Glad you got it working.[/quote]

thanks for the step by step write up and links... i am sure i am going to need it when i finish up my vr-4.