volkswagens-for-life

I know there's a trick and you need to adjust a sensor first. What is this trick?

DUB

Verify that your Throttle Position Sensor is adjusted to specs. Usually .54 volts (+/- .075 volts)

It all depends if someone got in and messed around with your idle set screw or not.

It is a bit more involved than what you may think...because it is wise to make sure that you have a scanner connected so you can read data when the engine is running. Just turning 'this and that' really does not work in this scenario. I do this for a living and you would NEVER catch me turning anything on a computer controlled engine without being able to verify what I was doing...was doing any good or not.

Trying to tweak your idle may actually be a vacuum leak and other issues that the scanner can aid in identifying (along with some other test equipment)...even though the computer is NOT setting a trouble code.

DUB

Z51breeder

Your idle is controlled by the car's computer/chip

volkswagens-for-life

Well ive done the stupid and tried adjusting my idle by the screw before I read that I shouldn't Have. I have bad idle problems with my car. It's probably the mail-order tune combined with the cam, but it could also be a vacuum problem or idle problem or just plain bad tuning due to lack of data. It's gonna be rough trying to figure out which one is causing poor idle.

Cold idle :
http://m.youtube.com/watch?v=nf_JV__QUP8


After she's up to temp:
http://m.youtube.com/watch?v=XjXW7nki4LE

fl_799

Yeah, best bet is to go through the basics of fuel pressure, checking for vacuum leaks, injector health, timing, checking the IAC function etc.

If those are covered, time to get into the computer and data log to see what the heck is going on. The computer will tell you everything you need to know to tune it.

Call me a skeptic, but it takes me days of solid data-logging to tune my cars, my fuel injected harley AND get it perfect. I have no idea how a mail order tuner can do this without some sort of log exchange and a few tries to nail it down. I used to help out members on the HDforum with tunes but only with a datalog with a twin scan 88.

volkswagens-for-life

Ya a mail order is terrible with this amount of mods I KNOW that it needs a live tune. You think it's more my tune than any Hard setting that's controlling my idle?


Also when warm it idles around 1200 to 1500 rpm lol

cudamax

You got your self a little slight popcorn Machine. I like the sound of that. Don't mess with the base Idle to much. Forget all that factry procedure. You don't have a stocker.

Go right to the throttle body and have someone or trap the thing to its floored position. Spray some carb cleaner right where the throttle sits at Idle. Thats where carbon builds and starts a ledge. Make sure its real clean.

Next get a water bottle or whatever u can come up with that u can squirt a real small stream of water into the engine {down the throttle or in the pcv valve hose} at about 2000 rpm don't let it die out while doing this and only a real little steady stream. Not a lot at once or you can bend a rod and screw up your motor.Try to get about 16oz thru the motor.

Make sure to get rid of any vacuum leak and advance ur timing as much as you can with out the thing destroying itself.

volkswagens-for-life

Thank you for the compliment.

As far as cleaning the throttle body. I did it with the car off but wasn't aware of the carbon ledge that forms. I'll give that a try again. I'll try the water stream idea also. Thank you for the suggestions. I'm also gonna get some ether and spray the motor and seals while it's running to try finding any vacuum leaks. If this all fails I reckon I'll have to wait for the dyno tune session.

cudamax

The TB and the TB bore plates fit in there with maybe .002 to .003 clearance and when its perfectly clean allows a small amount of air thru for a nice Idle. So the small clearance needs to be open or the IAC bleeds in more air to maintain idle and will/could hunt. Speeds go up and down. Make sure you have no vacuum leaks and TB clean before you go for a tune.
It's not really that bad and its might be running with low vacuum. Also check the 9th Injector fuse. Its hidden behind the dash. Some people like to pull them for some unknown reason. Its ur Choke. Shoots more in there for cold start enrichment

volkswagens-for-life

Ok I'm gonna go over the TB/blade with more scrutiny and maybe a plastic wire brush this weekend.

You dont think 1200-1500rpm is bad??? Thats 2x-2.5x higher than I hear most people idling at with their l98's lol.

cudamax

Cold thats still a bit high and Hot no way is that Acceptable. Even with a high duration overlap cam and no vacuum.
Get it down to about 800 to 850 in park. Your cam isn't that hot.

cudamax

If you want to go by the book. Here is another post I gave to someone else but in case case remove it and rinse the tit/pintal of all Carbon and clean the manifold passages completely where it goes in.

Check and replacing every single vacuum hose on that motor that might be leaking.
Replace sticking IAC and make sure it's fully extended/in its seated position by following this. Its a 1989 but should be the same
I purchased a 1989 corvette last year, and decided it was time to check the timing and clean the throttle body. Throttle body was removed, cleaned, and reinstalled with new gaskets. Replaced the Idle Air Control motor while I had it apart. Prior to starting this project, I noticed the TPS voltage was within spec but on the high side, and timing was not set to spec. Removed minimal air cap to adjust. Net results; improved get up and go, smoother running engine from idle to WOT, and better MPG (+3 highway, +2 around town). Provided are the documented steps I used. Some of the other posts on this topic are not complete (or incorrect), and the directions in the factory manual required a little refinement. I used an external tach that had a low setting with 20 rpm increments (Update: scanner works even better).

Start and run engine until it reaches operating temperature (closed loop)
Check and set ignition timing to 6 degrees before dead center (BDC) with tan EST wire disconnected
Check and set throttle position sensor (TPS) to .54 (+/- .08) volts at idle
Jumper terminals "A" and "B" on the ALDL
Turn ignition key on and do not start engine
Wait 60 seconds so that the idle air control (IAC) motor fully extends
Without turning ignition key off, remove connector from IAC motor
Turn ignition key off and disconnect ALDL jumper
Attach external RPM meter using Tach port or scanner using ALDL port
Start and run engine until it reaches operating temperature (closed loop)
Remove minimum idle air cap using awl if required
Adjust idle speed to 425 (+/- 25) rpm in either in park or neutral
Turn ignition key off and reconnect EST wire and IAC motor
Check and set throttle position sensor (TPS) to .54 (+/- .08) volts at idle
Reset ECM by disconnecting and reconnecting power at battery terminal
Depress accelerator pedal slightly
Start and run engine for 5 seconds
Turn ignition key off for 10 seconds
Drive vehicle to assist in ECM reprogramming
If you used a scanner, you should see around 20 IAC steps
Make sure TPS IS GOOD

volkswagens-for-life

I attached my sig so you can see cam specs.


Yes 1200-1500 warm . all depending on weather and who knows what else.

DUB

volkswagens-for-life,

I wish in your initial post you let us know actually that you did not have an original engine in your car.

Sounds like it is a FUN ride.

Other than that...one thing that I will add to 'cudamax's' information is that you might want to verify that your harmonic balancer is good....meaning...the outer ring has not spun...thus making you setting your timing with a light a bit FUN.

In a PERFECT WORLD...YES...but I guess all the Corvettes I have repaired that had a screwed up idle....both cold and hot.....I oddly enough did not have to replace a computer and or chip to get them running correctly...imagine that!

DUB

aklim

Jumping the terminals like Cudamax suggested, IMO, is only good for a bone stock unit. Once you get past bone stock, it is a crap shoot especially if someone screwed with the chip. On an 88, the TPS is adjustable. Fair enough. However, we don't know if the passages are clean or not. I always take off the IAC solenoid, take off the IAC housing, spray down the throttle body and the passages with brake cleaner. GENTLY wipe down the IAC and spray off the IAC housing. As with condoms, I don't reuse the paper gaskets. IAC or housing comes off, the gaskets get replaced. TB comes off, gasket gets replaced. I don't kike to spray stuff into the TB in an attempt to clean things. Kinda like cleaning a room in the dark. I take the TB off, take IAC off and IAC housing off. Bigger pain but I know that the TB is clean.

First thing is to ensure that there are no vacuum leaks and the timing is on. TIming is easy enough. I use a scanner to check IAC counts. If everything I do doesn't work and the counts are 0, I know there is a leak somewhere. Just did that. Turned out to be a plenum to manifold gasket leak in my case, among other bad hoses.

Also I set the idle to IAC counts. When the engine is in closed loop, I would shut everything but the motor down. See what the counts are. I shoot for 20 counts. If it is higher, I screw in the throttle body screw. If it is less I screw out the TB screw. Rev motor and wait for it to settle down and take a reading.

aklim

Post 4 he mentioned a tuned EPROM and post 13, he mentioned a cam.

volkswagens-for-life

Aklim: long time no speak man. I Haven't heard from you since bannation from cz28 years and years ago. Nice to hear from you!


Thank you for the compliments and YES, she scoots down the road at a scary rate of speed. This thing cruises at 120 more easily and surely than most cars I've driven can do 60.

Thank you guys so much for the ideas. Seems I have a LOT of groundwork ahead of me to fix this horrible idle issue. Thank you for the abundance of information and ideas all.

volkswagens-for-life

This is what happens when the car is cold. Slight Rev then does this super long popping. WTf?

http://m.youtube.com/watch?v=1WB6zOH1XJo

cudamax

Did you rev it twice and the 3rd time it dies? or did it do all of that after 1 rev?

DUB

Thanks.....I just did the one thing I hate...passed over an important post.

DUB