1990 Vett Problem
Thread Starter
Melting Slicks
Joined: Aug 2004
Posts: 2,052
Likes: 20
From: boston mass
1990 Vett Problem
My Frends Car Motor Is Stock No Work Done In 14 Years, Motor Shakes, And Hessitates While Driving, I'm Having Him To Being It To My Home As A Winter Project,
Question Will A Car Of That Year Show Codes?
3 Years Ago He Did Take It To The Dealer After 2 Days They Coundn't Find The Shaking And Stalling Problem. I Went With Him To Get The Car And We Saw 1 Reason They Coundn't Fix It Because They Had 2 Kids With The Service Manual Opened On The Hood Stairing At It. Would You Beleave They Tryed To Charge Him For That, He Got Mad A Took His Car Out Of The Bay And Told Them What To Kiss. (never Payed)
Question Will A Car Of That Year Show Codes?
3 Years Ago He Did Take It To The Dealer After 2 Days They Coundn't Find The Shaking And Stalling Problem. I Went With Him To Get The Car And We Saw 1 Reason They Coundn't Fix It Because They Had 2 Kids With The Service Manual Opened On The Hood Stairing At It. Would You Beleave They Tryed To Charge Him For That, He Got Mad A Took His Car Out Of The Bay And Told Them What To Kiss. (never Payed)
Le Mans Master
Joined: Oct 2000
Posts: 6,362
Likes: 30
From: Oak Harbor WA
Post this in the C4 section for more replies. This is the C5 section. That sounds like a miss and it may or may not set a code simply because it is older technology and it would just depend on what the error is. If it is monitored by a sensor it will set a code. If it is a bad plug then it might not. You may get something else related to it like a lean or rich condition.
Poor idle performance can be a multitude of things:
Bad gas
Vacuum leak
Poor spark (wires and plugs)
Poor tune up (timing)
Blown head gasket
Timing chain slipped
lifter malfunction
poor valve spring function
throttle body gunked up
power enrichment slow to react
clogged injector(s)
No work done in 14 years??
If that is true I'm surprised it still runs at all. 
Your friend should be happy the service techs had the service manuals out. If you work on it without the Helms manuals are you any better then them? The manuals are there for a reason, not something to collect dust with. You think they have all these different manuals memorized? A dealership can have a car for a couple of days because they aren't going to just drop everything they are doing to start a new car. They clear out the customers on a first come first serve basis. Now if you called ahead to make an appointment I can understand being a bit peeved. Car repair takes troubleshooting at times because the fix isn't so obvious more often then not especially as cars have become more complex......maybe they were out of IBM Pixie dust.
Poor idle performance can be a multitude of things:
Bad gas
Vacuum leak
Poor spark (wires and plugs)
Poor tune up (timing)
Blown head gasket
Timing chain slipped
lifter malfunction
poor valve spring function
throttle body gunked up
power enrichment slow to react
clogged injector(s)
No work done in 14 years??
If that is true I'm surprised it still runs at all. Your friend should be happy the service techs had the service manuals out. If you work on it without the Helms manuals are you any better then them? The manuals are there for a reason, not something to collect dust with. You think they have all these different manuals memorized? A dealership can have a car for a couple of days because they aren't going to just drop everything they are doing to start a new car. They clear out the customers on a first come first serve basis. Now if you called ahead to make an appointment I can understand being a bit peeved. Car repair takes troubleshooting at times because the fix isn't so obvious more often then not especially as cars have become more complex......maybe they were out of IBM Pixie dust.
Race Director
Joined: Nov 2003
Posts: 12,346
Likes: 5
From: Mustang OK
Yes, the people over in C4 Tech/Performance would be in a better position to help you than here in C5 Tech. Good luck with the fix. 
Tech Contributor
Joined: Dec 1999
Posts: 32,910
Likes: 2,402
From: Anthony TX
CI 6,7,8,9,11 Vet
St. Jude Donor '08
I forget if that car has OPTI Spark or a standard Distributor. The very first thing that you need to do is change the plugs and wires. If you do not change the wires, at least check them with an ohm meter. They should rear 2000-3000 ohms.
OBD1 cars will show codes and all you need to do to read them is jumper terminals "A" + "B" together with a piece of wire and the "CHECK ENGINE" light will flash out the codes. First code that you will see is a 12 code which is normal and will always be displayed. It flashes each code three times and then moves on to the next code. It wil end the code session by flashing the 12 code again three times.
If the car has been running that bad for that long, you may have BAD CAT"S If they are clogged up the car will idle fine but will not run well or at all at higher RPM.
You should get lots of help in the C4 section. If not, you can PM me. I use to have an 85 coupe!
OBD1 cars will show codes and all you need to do to read them is jumper terminals "A" + "B" together with a piece of wire and the "CHECK ENGINE" light will flash out the codes. First code that you will see is a 12 code which is normal and will always be displayed. It flashes each code three times and then moves on to the next code. It wil end the code session by flashing the 12 code again three times.
If the car has been running that bad for that long, you may have BAD CAT"S If they are clogged up the car will idle fine but will not run well or at all at higher RPM.
You should get lots of help in the C4 section. If not, you can PM me. I use to have an 85 coupe!
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Top 10 Most Expensive Corvettes Ever Sold on Bring A Trailer
Brett Foote
10 Things Every Corvette Owner Needs (2026 Edition)
Michael S. Palmer
8 Most "Only Corvette Owners Understand" Quirks and Problems
Pouria Savadkouei
10 Reasons the C6 Z06 is Still A Performance Benchmark After 20 Years
Joe Kucinski
How Much Horsepower Every Corvette Engine "LOST" in 1972
Joe Kucinski
Top 10 DOs and DON'Ts for Protecting Your Convertible Top!
Michael S. Palmer
Top 10 Most Explosive Corvettes Ever Made: Power-to-Weight Ratio Ranked!
Joe Kucinski
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Thread Starter
Melting Slicks
Joined: Aug 2004
Posts: 2,052
Likes: 20
From: boston mass
Originally Posted by Bill Curlee
I forget if that car has OPTI Spark or a standard Distributor. The very first thing that you need to do is change the plugs and wires. If you do not change the wires, at least check them with an ohm meter. They should rear 2000-3000 ohms.
OBD1 cars will show codes and all you need to do to read them is jumper terminals "A" + "B" together with a piece of wire and the "CHECK ENGINE" light will flash out the codes. First code that you will see is a 12 code which is normal and will always be displayed. It flashes each code three times and then moves on to the next code. It wil end the code session by flashing the 12 code again three times.
If the car has been running that bad for that long, you may have BAD CAT"S If they are clogged up the car will idle fine but will not run well or at all at higher RPM.
You should get lots of help in the C4 section. If not, you can PM me. I use to have an 85 coupe!
OBD1 cars will show codes and all you need to do to read them is jumper terminals "A" + "B" together with a piece of wire and the "CHECK ENGINE" light will flash out the codes. First code that you will see is a 12 code which is normal and will always be displayed. It flashes each code three times and then moves on to the next code. It wil end the code session by flashing the 12 code again three times.
If the car has been running that bad for that long, you may have BAD CAT"S If they are clogged up the car will idle fine but will not run well or at all at higher RPM.
You should get lots of help in the C4 section. If not, you can PM me. I use to have an 85 coupe!
Safety Car
Joined: May 2003
Posts: 4,961
Likes: 2
From: Vette-hid.com Lost in DFW texas
Cruise-In V Veteran
Cruise-In VI Veteran
Cruise-In VII Veteran
St. Jude Donor '06-'07
as a ex c4 owner i would do this
Plugs and wires cap rotor
replace fuel filter and check pressure running 38psi
Clean throttle Body they are always nasty on a C4 tpi car
it is more than likely not a computer related issue.Spark/fuel/or air intake system. Doesn't hurt to replace the IAC valve on throttle body they get sticky.I used to tear the top intake off my c4 all of the time when i first got it.PM if if you need any help.
Plugs and wires cap rotor
replace fuel filter and check pressure running 38psi
Clean throttle Body they are always nasty on a C4 tpi car
it is more than likely not a computer related issue.Spark/fuel/or air intake system. Doesn't hurt to replace the IAC valve on throttle body they get sticky.I used to tear the top intake off my c4 all of the time when i first got it.PM if if you need any help.
You can PM me also! 
