1991 L-98 rough idle

[yellow91]

I have a 1991 corvette L98 auto, I have changed the Ignition Control module; coil; spark plugs and wires; cap and rotor; cleaned entire intake system inside and out from the throttle body to the manifold; new IAC valve, set TPS sensor to .54 volts at idle (car idles at 690-720 rpms); EGR system fine; computer reads fine: ignition timing set at 6 degrees before TDC; compression check (165-180 all cylinders) plus it doesn't consume a drop of oil; new fuel pump and filter; injectors resistance at 16.5 on all injectors; and rebuilt tranny and new torque converter.

The problems I have are rough idle, car tries to stall when I accelarate slowly (only when I first start out after letting it warm up), and if I have low fuel level when the range on the computer is at 30-90 miles it will want to die or it misses when I WOT it.

The only things I can think of left to fix is maybe new computer, oxygen sensor, clean or replace injectors, or maybe I need to replace fuel pump strainer which was falling apart when I did the pump. I didn't bother to replace it a the time.

Please help

 

[Moonunit 451]

I'm not clear if you replaced the inline fuel filter, and I can't imagine how you replaced the fuel pump without repalacing the screen . That shoud be a given and could let unknown amounts of crap to move into your fuel filter. Looks like you've done a lot of other stuff. How many miles on your car? Did you do an injector leak down?
Just my thoughts.

 

[Eagle85C4]

Have you checked the Idle Air Control (IAC)? It is screwed into the throttle body on the passenger side just below the TPS. Remove it and see if it is covered in gunk. Be very careful when cleaning it per the manuals...

 

[Edmond]

If it is the oxygen sensor or ECM, you will get a SES light on. You said the computer isn't reading anything so I think you could rule out the O2 and ECM.

 

[Daryllawman]

Not on my Vette but on my police cruiser I had the same problem and they thought it was a bad injector but it turned out to be a coil pack. They had it all day at the police garage......Have you looked at that?

 

[yellow91]

Yes I did replace the inline fuel filter. I bought a new IAC valve and clean the entire throttle body. My car has 135,000 miles all with 7 original injectors and 1 replaced, not sure when or why. I bought the car at 125,000. One thing that could lead me to a leaky injector is one time I drove up to my friends house, after awhile we decided to go for a drive, the car car started fine and I backed out and it stalled on me, started it again and same thing it stalled so about 5 or 6 times later the car wouldn't start at all. After an hour of waiting we attempted to try again, it started and drove fine. It still stalls on me once and awhile. That was before I took the manifold off and cleaned everything, now it still stalls on me sometimes when I pull out of a parking lot, I'v set the TPS to .54 and reset the new IAC. Is .54 at the TPS corrected by setting screw ( it's the only way)

 

[vets4-2]

pull the codes you'll probable get #41 02 sencer but with that many miles(and that's alot) start thinking about a rebuild."LIKE NOW"!!!! Your car's engine life is over!

 

[Eagle85C4]

Not so fast there my friend.....my 85 has 147,000 does not smoke and has 165-175 psi on each cyl. Milage has nothing to do with it if...and a big if... the engine has been taken care of on a regular basis and not driven to death....I got a chevy Blazer with over 200,000 on a stock 305...just now started to smoke first thing in the morning...valve seals. My Porsche has over 300,000 miles on the original engine....take care of them and they will last...

 

[yellow91]

thank you eagle85c4, your right but my dad is a gm mechanic (60s-70s, so he can't help me with the computer stuff) and when I pulled the valve covers and intake he said that the engine has been rebuilt or at least the top end, but remember my car doesn't eat a drop of oil, not even after 5000 miles between my last oil & filter change. I use 20 50w and next oil change I will use Mobile One 10 40w to see if it will leak or burn. My engine runs strong and has great performance but just that rough idle and sometimes stalling drives me crazy.

Is there a way to pull codes from the computer without scanning tool.

I might go with Moonunit 451's idea and test the injectors, i'v tested them for resistance, but how can I test them for leaks or clogs. I don't want to dump anymore money into this car by having to bring it to a shop.

 

[yellow91]

and my compression test shows 170-180 across the board on all cylinders.

 

[Edmond]

Is there a way to pull codes from the computer without scanning tool.

Yes:
with the vehicle off,
jumper the top two ports on the right with a paperclip
the port is below the steering column, just a little bit to the right
after you've jumped the ports, turn the key on but don't start the car

look at the SES light on the information console
count the number of flashes
each code is comprised of two numbers and each code will flash 3 times

for instance, you get a flash of

1 2 (one flash, then two flashes)
1 2 (same as above)
1 2 (same as above)

that's normal and means that nothing is wrong

count the flashes and let us know, we'll look it up in the book and tell you.

 

[Eagle85C4]

Edmond ya forgot to tell him about the ADL and where it was....
Look under the dash on the drivers side above the gas pedal...there you will find the ADL...the last 2 " holes on the right, jumper with a paper clip, top and bottom on right, then turn on key but do not start...watch the service engine light...it will begin to blink....one flash...pause then 2 flashes =12, it will do that three times. Anything after that is an error code, write it down, finally it will flash the 12 again three times and start over. let us know what you find...

 

[Edmond]

You know Eagle, when the SES light comes on in the Corvette, I don't panic anymore because I know I can pull the codes myself. But when it comes on in the Toyota, I curse to myself and say, "There goes another $80" because they didn't design the car to let you pull the codes off yourself. Even though it's OBDII, it's a different plug so you have to go back to the Toyota dealership.

 

[Eagle85C4]

I know what you mean Brother....it used to worry me until I copped an attitude....then I just started taking it apart till I figured it out and in the mean time I learned all there was by doing so....can't be afraid to tackle a job....there are no problems....just challenges...take care man...

 

[Mr. Corvette]

Fuel Injector testing

Testing Fuel Injectors:

Get an Ohm meter or VOM meter.

1. Turn on the car
2. Unplug one of the wires from one fuel injectors
3. Connect Ohm Meter lead to connectors on the fuel injector.
Readings should be: 14 Ohms or less for a good injector.
Any reading higher than 14 Ohms indicates
that the fuel injector needs to be replaced
with a new one.
4. disconnect Ohm meter.
5. reconnect wire to fuel injector.
6. Repeat procedure on all eight injectors.

Never use a fuel injection cleaner with the 1990-1991 L-98 engines the cleaner will ruin the injectors.

The injectors usually go bad in series, all of the injectors should be replaced with new according to a Chevrolet Dealer Service center cost is around $1,100 - $1,400 with a lifetime warranty on the new fuel injectors for as long as you own the Corvette.

The Fuel Injectors used by GM in 1990 and 1991 were crap according to a local Chevrolet Service Department. All 1990 - 1991 Chevrolets fuel injectors will need to be replaced due to a poor design.

My former 1990 Corvette with L-98 engine with less than 8,000 miles had gone through 12 fuel injectors within four years.

 

[yellow91]

thanks mr. corvette, are you sure about the 14 ohms resistance. I got 16.3-16.5 on all injectors. All my injectors are original except one, not sure when it was replaced. If 14 is right then you might have just solved my problems, do you think I can use ACCEL replacement injectors at $240 for the set. I'm not about to spend a thousand or so dollars more on this car. Don't get me wrong I love this car but can't afford now, I need new tires and those are a thousand dollars.

 

[Edmond]

New tires???

Get the Firestone SZ50's, they're great!

 

[yellow91]

thats what tires i'm going with, whats the price.

 

[yellow91]

wow, my injectors resistance is now 18.2 instead of 16.5 as of 3 month ago, you must be right mr. corvette.

 

[Edmond]

thats what tires i'm going with, whats the price.

I paid $186 a piece at Tirerack.

Do you have the Bosch injectors?