sweetmelissa

My car seems to be sucking down the gas badly !! Also seems there's a bit of a high idle (at times), not too bad but it's there. Can (sometimes) be driving and take my foot off the gas and it goes by itself and eventually it kicks down. When I come to a stop it sits at a perfect idle... looked everywhere for a vac leak !! Also if I'm going 45 mph I'm tacking around 1500 rpm's ( is that good ) ?? It's an 89 Iroc with a tuned port 350 L98,, completely stock !!!! Do the 350's normally suck down the gas rather quickly ? Is that bit of a high idle (at times) playing a role in gas guzzling ??

Tuned Performance

iTrader: (92)

The Car driving it self is more than likely the throttle shaft is worn in the throttle body and hanging up. You can check for play bye manually opening the throttle blades to around 1/4 throttle and check for movement up and down and back and forth while holding the throttle arm. Over time the throttle shaft wears into the throttle body housing. There are no bushings to help prevent wear like carburetor have. As far as the gas milage you should be in the 18-23 range depending on driving habits and conditions.

sweetmelissa

Thanks tuned performance,, It didn't occur to me to look at the throttle shaft !! I'll check that next !

sweetmelissa

TunedPerformance,,,,I checked the throttle shaft and it appears good..What I did notice was inside the plenum is dirty (black, greasy carbon)..Wasn't aware it was that bad.. I was thinking maybe those two butterflies (I call them) are getting stuck from all that crap especially when the engine heats up and not opening and closing like they should..I'm gonna clean out that plenum first,, any product in particular you recommend for that ? Do you think this may be my problem ? When I clean it out I want to run the engine and spray cleaner directly in plenum with butterflies open,, right ? I do a lot of things on my car by myself and looking for a little guidance..

Also, I replaced my O2 sensor a couple months back (threw a code) and couldn't believe it was the original factory one,,, made a huge difference in my engine performace.. Do you think all that crap in my plenum was from that old O2 sensor??? When I finally get that plenum cleaned out do you think that my car won't be driving by itself anymore ?????

Thanks for your help !!!

Melissa

jas2730

iTrader: (7)

That carbon build up is coming from your egr valve or your pcv and can definitely cause the butterflies to hang open. Give the throttle body a good cleaning and see what happens. I have a Dodge Durango that needs cleaned often or it gets stuck.

jas2730

iTrader: (7)

No on having the engine running while cleaning. 2 reasons why. 1, you'll need to manually open the butterflies to clean them. If the engine is running you'll be revving the crap out it and sucking whatever junk is floating around into the engine. 2, chances are whatever cleaner you choose will be flammable and could ruin your day real fast.

Tuned Performance

iTrader: (92)

It sounds like a bunch of carbon on the iac pintle tip and or passage wich is in the verry center of the throttlebody. I use castor oil super clean while the throttle body is off to cut the carbon and grease. carb and choke cleaner works great too. you might want to remove the iac and clean the passage. I hate to tell anyone to remove the lower iac plate. Most often because coolant is running through the plate the screws corrode and often time atleast 2-3 snap off . I have had to weld on nuts to extract the broken off piece left behind. so unless you can have some down time dont fool around with removing the iac plate.

http://www.autozone.com/autozone/par...96537&cmpid=cj
http://chevythunder.com/do_it_yourse...ation_page.htm

jas2730

iTrader: (7)

A small Christmas tree shaped, plastic bristled brush will help break it up.

Tuned Performance

iTrader: (92)

or use your spouses tooth brush

jas2730

iTrader: (7)

sweetmelissa

O.K. I see !! take the plenum "out" and clean it !! this shouldn't be difficult,,and don't touch the lower IAC plate !!!!

Thanks TP

jas2730

iTrader: (7)

TP! Lol. The crud inside the plenum you can live with. The stuff in the throttle body is what you need to address.

sweetmelissa

LOL !! No spouse !!!

jas2730 thanks for also chiming in !!!!

jas2730

iTrader: (7)

Np. Your welcome.

sweetmelissa

O.K.

jas2730

iTrader: (7)

You can repay me by posting some pics of your ride. I'm a sucker for IROCs.

sweetmelissa

Jas, I can't figure out how to post pics !! I could however send you (If you know how) some pics and even a video from my phone and then you could post em up for me !! ..I can text them to you from my phone... will that work ?? Or maybe someone on here knows how to do it if I send pics and video directly from my phone to theirs.....

jas2730

iTrader: (7)

Upload your photos to photobucket. Click on them to enlarge, then right click them, select copy then paste them to your post. There's also a photobucket app for your mobile device that allows you to upload to your account directly from your phone.

jas2730

iTrader: (7)

Then you can post huge photos. lol

jas2730

iTrader: (7)

If you don't have any success Pm me and i'll give you my cell#.

jas2730

iTrader: (7)

Any news? Did you get it all shiny and clean?

sweetmelissa

Yup,, It's nice and clean but still have that driving by itself, high idle !! It runs too good to be the egr so I don't think it's that. Tunedperformance really got my attention when he said that's where the carbon can come from...I'm looking everywhere for a vac leak,, can't find it !!! Any other things I should be checking ?????

Also when I was under the hood I listened to my injectors (fairly new) !!!
I took a piece of wood,, the kind you stake your property lines with,, about 2 ft long and held it on an injector and place my ear on the other end and listened.. Really cool how you can hear what's going on !!!!!

So, what should I do next ???

sweetmelissa

Sorry,, it wasn't TP that said carbon can come from egr,, it was Jas......

Tuned Performance

iTrader: (92)

If the egr was stuck open your idle would be low and the engine would almost die. There are two more thing I would look at the base timing with the est disconnected 6dbtdc and set the minimum idle speed with the iac commanded in and then readjust the tps. Although you have checked the engine for vacuum leaks , try blocking the vacuum booster vacuum line, you could have a internal vacuum leak in the booster or even in the hvac line.
http://www.iroczone.com/2009/10/adju...ir-idle-speed/
http://www.iroczone.com/2009/10/adju...on-sensor-tps/

sweetmelissa

O.K. Thanks TP !!!!!

Tuned Performance

iTrader: (92)

I hope Im on the right track, the sticking idle is odd like the throttle cable is binding but on tpi the sharpest bend is the one going through the bulk head to the pedal. Not sure what to tell you unless the coolant temperature sensor is causing the high idle and telling the ecm the engine is cold and dumping more fuel into the engine. Know of anyone with a obd1 hand held scanner ? Or buying a aldlcable from aldlcables.vom and using tuner pro you might be able to see the issue. the 1227165 ecm can be a real pain to connect to though.

sweetmelissa

Cooling temp sensor is fairly new but I will definitely have it checked (never know)... My plenum gets pretty hot also,, don't know if that's normal or not!!! Don't remember it ever getting that hot,, usually after a good ride it is cool to touch.. It is summer and the temps here have been 95-100 everyday I thought maybe that has something to do with it !

Yea, I do know someone who has a $14,000.00 dollar scanner (the size of a laptop) and he types in ANY vehicle year and it tells everything about the engine, he also very good with the tpi's and he has free diagnostics... He is 4 towns over from me,, I'm gonna have to take the ride over.. Today I have thunderstorms and downpours and the Iroc does not go out in the rain so will go tomorrow....I showed him my car last summer and he offered me $10,000.00 for it right then (cash).. I said nope, not for sale !!

I hope I don't do any damage to my car driving it like that !!! What do you think ? Will I be o.k. ?

jas2730

iTrader: (7)

As long as your temps are normal and it seems to be running ok you shouldn't hurt it. As far as the plenum, it should be cool to the touch. I don't know what would cause it to get hot. Maybe your timing is advanced to much?

sweetmelissa

Yup, temps are normal !!!! So, you think my car jumped timing ???? That's never happened to me before !!!!! What makes and engine jump timing ????

jas2730

iTrader: (7)

I'm not sure if your timingis the culprit. But if your distributor hold down is a little loose it couldlet your distributor move a little.

sweetmelissa

o.k... I'll take off the cover and check for any looseness.....

sweetmelissa

Took my car for a check up, apparently my IAC needs to be replaced !! Was advised to buy the new valve at a chevy dealership (OEM part) and not the auto parts store because they are reman and made like crap and I'd have to keep replacing them...

TP, you were right when you first said a clogged IAC,, although it may not be clogged the IAC is definitely a problem.....Also, these cost around $100.00 at the dealership.....I chose to fix it myself and left the mechanics with a printout on how to reset the IAC ......

Tuned Performance

iTrader: (92)

Goto rockauto.com and lookup the acdelco part number than search ebay

sweetmelissa

O.K. Thanks TP

89mulletbird

iTrader: (4)

It's very important to have your idle air screw set properly or your IAC may be "bottoming" out, resulting in your engine getting too much air (causing high idle).

The idle air screw is the screw that stops your throttle from closing all the way.

To set this properly you need a diagnostic device that can read your IAC position. When your car is fully warmed up, you need to adjust your idle air screw until your IAC position is between 20-30.

If you want to do this the crude way you can look at this page:
https://www.thirdgen.org/tpimod2

Also, you must regularly clean the carbon from the throttle body if you have alot of miles on your engine. When I had a stock TPI car, I had to do this every 1-2 months because the PCV valve put so much carbon into my intake.

sweetmelissa

Here is the reset instructions I got from mechanic !!!

1. block drive wheels and apply parking brake.

2. start engine and hold engine speed above 2000 rpm. Ground the diagnostic test terminal (ALDL) for ten seconds, the remove the ground.

3. Turn the ignition "OFF" then restart the engine and check for proper idle operation.

The IAC valve may also be reset by the ECM when the vehicle is driven at a speed above 40 mph. The ignition may have to be cycled OFF and ON a few times before proper idle can be obtained......

does this seem right ?

89mulletbird

iTrader: (4)

Well, he doesn't mention anything about properly adjusting the IAC screw. I'll look in my GM manual today and scan the page.

sweetmelissa

The information is from a printout he gave me,, from a site called
alldatapro.com

sweetmelissa

TP,, had to order an IAC valve from chevy dealership.. It cost $165.00 but the "nice guy in parts dept." gave me a deal and hosed me for $125.00...Atleast I have a brand new ac delco......

Isn't the pintle suppose to move up and down ?? The brand new one does not.. Does it have to be installed first for that to happen ??

Schrade

Do you have any DTC codes?

Don't spend money on parts until you KNOW that they're bad. Biggest racket in the auto repair industry. Test for voltage TO the part, and test the ground FROM the part.

Get EVERYTHING, every step of the way, IN WRITING! Mechanic says you need a new IAC??? "Show me, and put it in writing why you think that.

Vacuum leak (or just plain air) can't be seen. Not by yours truly, anyway... I saw a sneeze once, but only because of the green jam that accompanied the 'flow'. And that was OUT, not IN!

You probably don't have a vac leak anyway. These things usually cause warmed-up idle rpm's to swing rhythmically.

Broken O2's, or broken temp sensor will make injector pulsewidth stay pegged, and will foul cats in short order.

Get codes. If none, get a datalog printed out from a shop and posted up here on the boards.

Tuned Performance

iTrader: (92)

WOW, that's alot for a iac. The iac is a motor and moves the pintle jack screw .
It will have good resistance if you try to push it in to set the installed length.
If it was installed with the pintle extended to much this will destroy the iac.
To see if the iac is being commanded you can buy a iac noid light.

Tuned Performance

iTrader: (92)

http://chevythunder.com/do_it_yourse...ontrol%20Motor

http://www.ebay.com/itm/9-ELECTRONIC-FUEL-INJECTION-NOID-LITE-SET-SIGNAL-TESTER-/190458199839?pt=Motors_Automotive_Tools&hash=item2c58317f1f&vxp=mtr

sweetmelissa

TP, does a bad temp sensor make the plenum too hot ?? If not, what does ??

Tuned Performance

iTrader: (92)

the tpi plenums are a giant heat sink There is nothing I know of that you can do to cool it down. ice bags will get expensive lol

Schrade

No.

A bad temp sensor could make the ECM think the, motor is still cold, and make the injector pulsewidth stay pegged, and actually run COOLER, with a SATURATED burn.

A LEAN burn will make the motor run hot.

Tuned Performance

iTrader: (92)

Motor I thought we were talking about a engine
So your saying a bad mat or cts will cause the injectors to be at 100% duty cycle Where does one come up with this kinda of information ?

89mulletbird

iTrader: (4)

Have you checked the timing? If its too far retarded, it will run hot and have poor fuel economy.

Schrade

(tell ya' a quick story about, "So you're saying..."? ... I once got deposed by the bad guys lawyer, without my own counsel. He asked me some questions, and didn't get what he wanted to hear. So he says, "So you're saying...?". I looked at the person doing the video / audio recording, and told them to play back my previous response. THAT'S WHAT I SAID. Pi55ed him off, cause he never had run into the likes of MY smarts ).

Anyway...

I DO think I have it backwards.

But now, you seem to have LOTS of questions.

Why not just say what you know?

I suggested once before; maybe just post solutions to OPs' problems.

vetteoz

iTrader: (13)

Not what you said in the O2 post a couple of days ago
Maybe you are just making this stuff up as you get corrected ?

vetteoz

iTrader: (13)

Instead of only 3rd Gen experiences like you do ?