85 running rough
Thread Starter
Racer
Joined: Sep 2003
Posts: 322
Likes: 0
From: Gap PA
85 running rough
Well, the 85 started to run and idle rough.
Changing plugs, wires, cap and rotor was on the winter list anyway, so I did that and it still runs the same. I checked to make sure I had everything hooked up correctly and I do. It starts right up with no hesitation at all, so I must have gotten that all back together otherwise it would hardly run.
What would by all of yours next step?
I know I'm not the only one that has went down this road before.
Changing plugs, wires, cap and rotor was on the winter list anyway, so I did that and it still runs the same. I checked to make sure I had everything hooked up correctly and I do. It starts right up with no hesitation at all, so I must have gotten that all back together otherwise it would hardly run.
What would by all of yours next step?
I know I'm not the only one that has went down this road before.
Thread Starter
Racer
Joined: Sep 2003
Posts: 322
Likes: 0
From: Gap PA
The old plugs looked a bit oily. I have no clue how long they had been in there before I owned the car
This does not suprise me knowing I need new valve seals. (also on the winter list)
I did not clean out the throttle body yet. That is why I was asking what everyones next step would be!!
There have been no codes thrown.
This does not suprise me knowing I need new valve seals. (also on the winter list)
I did not clean out the throttle body yet. That is why I was asking what everyones next step would be!!
There have been no codes thrown.
Racer
Joined: Dec 2006
Posts: 292
Likes: 0
Well, the 85 started to run and idle rough.
Changing plugs, wires, cap and rotor was on the winter list anyway, so I did that and it still runs the same. I checked to make sure I had everything hooked up correctly and I do. It starts right up with no hesitation at all, so I must have gotten that all back together otherwise it would hardly run.
What would by all of yours next step?
I know I'm not the only one that has went down this road before.
Changing plugs, wires, cap and rotor was on the winter list anyway, so I did that and it still runs the same. I checked to make sure I had everything hooked up correctly and I do. It starts right up with no hesitation at all, so I must have gotten that all back together otherwise it would hardly run.
What would by all of yours next step?
I know I'm not the only one that has went down this road before.
Thread Starter
Racer
Joined: Sep 2003
Posts: 322
Likes: 0
From: Gap PA
The more I research (and based on the Haynes Manual), the fuel filter is the next change. Most likely needs one anyway.
And I hate to sound dumb, but what is IAC? I prob know what it is, I am just not familiar with the initials.
And I hate to sound dumb, but what is IAC? I prob know what it is, I am just not familiar with the initials.
Burning Brakes
Joined: Aug 2005
Posts: 1,152
Likes: 1
From: It's Bad Ass in Black! Cape Coral, Florida
I have an 85 automatic, try this tech tip.
https://www.corvetteforum.com/techti...D=55&TopicID=2
How old is your gas? Fuel filter is a start for sure. I would also recommend a can of Sea foam in the gas tank. What kind of spark plugs did you put in? Hopefully not Bosch +4 as they made mine run rough. Switched to NGK Platinum, much better.
https://www.corvetteforum.com/techti...D=55&TopicID=2
How old is your gas? Fuel filter is a start for sure. I would also recommend a can of Sea foam in the gas tank. What kind of spark plugs did you put in? Hopefully not Bosch +4 as they made mine run rough. Switched to NGK Platinum, much better.
Le Mans Master
Joined: Feb 2006
Posts: 8,753
Likes: 9
From: Louisiana
Go ahead and install a new fuel filter if you have no idea how many miles is on that one. A fuel pressure guage is a handy tool to have along with a volt/ohm meter, test light, noid light, and a factory service manual.
The IAC (idle air control) is mounted in the bottom of the throttle body. The air passage becomes carbon filled and so does the IAC. You have to remove the TB to get to the IAC. Clean both with throttle body cleaner and a toothbrush.
Without any codes, I would work on the items that won't throw codes first.
The IAC (idle air control) is mounted in the bottom of the throttle body. The air passage becomes carbon filled and so does the IAC. You have to remove the TB to get to the IAC. Clean both with throttle body cleaner and a toothbrush.
Without any codes, I would work on the items that won't throw codes first.
Thread Starter
Racer
Joined: Sep 2003
Posts: 322
Likes: 0
From: Gap PA
I put in AC Delco's.
The gas isn't that old, I have been driving the car all summer, and it just started acting up one random Saturday afternoon.
I haven't had much time to invest in working on it, since it happened right before Xmas and I had to travel home and once I got back it was a week and a half. I should be able to get this straightened out quick.
Thanks for the info guys. I will keep you informed.
The gas isn't that old, I have been driving the car all summer, and it just started acting up one random Saturday afternoon.
I haven't had much time to invest in working on it, since it happened right before Xmas and I had to travel home and once I got back it was a week and a half. I should be able to get this straightened out quick.
Thanks for the info guys. I will keep you informed.
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Racer
Joined: Jun 2001
Posts: 377
Likes: 10
From: Chicago IL
I agree with the thoughts above. Another quick thought is bad maf so, unplug maf and see if the car runs better or worse - if the car runs better, you probably found your problem (get ready to clean out your wallet). Also, I forgot to plug in electrical connectors to the air pump on some reassembly adventure and the car was really rough. so i would give car a nice once over to make sure all connectors are plugged in, vacuum hoses etc. Oh yeah, lets hope it isnt that maf burn off module (unique to 85) behind the bread box. I have no idea how to test that but I know that part is insanely expensive. check for vacuum leaks too.
Thread Starter
Racer
Joined: Sep 2003
Posts: 322
Likes: 0
From: Gap PA
Well, I have spark, I changed my fuel filter and it still runs rough.
I did, however, find that the right side exhaust manifold gets significantly hotter then the left side, leaving me to believe I still have a fuel problem.
After about 30 seconds of running, I could hardly put my hand on the heat shield on the right side, but could easily grab onto the left side heat shield.
Plugged fuel rail?
I did, however, find that the right side exhaust manifold gets significantly hotter then the left side, leaving me to believe I still have a fuel problem.
After about 30 seconds of running, I could hardly put my hand on the heat shield on the right side, but could easily grab onto the left side heat shield.
Plugged fuel rail?
Le Mans Master
Joined: Sep 2006
Posts: 6,050
Likes: 147
From: Phoenix AZ
2021 C4 of the Year - Modified Finalist
cold pipe
It's possible the left precat is plugged up or a baffle inside broke loose and is partially blocking the exhaust path
Id take off the exhaust, or loosen it up sufficiently so that it leaks really bad, and start the car up momentarily and see if it runs better.
If no precats, It could be a bad O2 sensor out of range but still in the computer's criteria
but I'd go with the exhaust because cold pipes usually mean restriction
Id take off the exhaust, or loosen it up sufficiently so that it leaks really bad, and start the car up momentarily and see if it runs better.
If no precats, It could be a bad O2 sensor out of range but still in the computer's criteria
but I'd go with the exhaust because cold pipes usually mean restriction
Last edited by coupeguy2001; Jan 11, 2007 at 08:10 PM.
Thread Starter
Racer
Joined: Sep 2003
Posts: 322
Likes: 0
From: Gap PA
The only cat on the 85 is the one in the middle of the car under the tranny.
And why would a plugged cat cause the exhaust manifold at the engine to be cold? Where would the exhaust be going then?
And why would a plugged cat cause the exhaust manifold at the engine to be cold? Where would the exhaust be going then?
Le Mans Master
Joined: Feb 2006
Posts: 8,753
Likes: 9
From: Louisiana
Yep, no precats on the 85 stock. I would check the EGR at the right rear of the intake manifold. You will need a vacuum guage that can apply pressure and a FSM to follow the troubleshooting steps.
EDIT: also check the vac lines going to it and the solenoid/temp sensor.
EDIT: also check the vac lines going to it and the solenoid/temp sensor.
Last edited by RRT vette; Jan 11, 2007 at 09:56 PM.
Instructor
Joined: Dec 2006
Posts: 213
Likes: 0
From: sparta michigan
I would start by checking codes, I went down this road and had a intake air leak code stored, hooked up to a scanner and my o2 sensor was very erratic, so for $25 I swapped it out and fixed the rough running.
Le Mans Master
Joined: Sep 2006
Posts: 6,050
Likes: 147
From: Phoenix AZ
2021 C4 of the Year - Modified Finalist
cold pipe
well, sowweeee.
If the exhaust pipe is cold, that should be a clue.
I have a 85 Y pipe on my engine run stand,, and I should have looked at that b 4 commenting...Duh.
1. Air pump r/h diverter valve bad? remember the diverter valve is
supposed to open to the exhaust when cold, then divert to the cat
when warmed up? could point to a vacuum leak? no control pressure?
could be working on the left, but not on the right?
plugged up R/H check valve, or failed check valve
2. Fuel.....unlikely, but possible,
fuel rail restriction
fuel rail transfer tube clogged
fuel pressure regulator problem
restricted fuel return line back at the tank
fuel pump pick-up screen clogged
3. Electrical.......
broken wire on diverter valve
Bad temp switch in the front of the manifold? Engine stays in
cold open loop all of the time?
leaking cold start valve (on the left side)
cold start valve temp switch stuck in enrichment
4. anybody's guess
If the exhaust pipe is cold, that should be a clue.
I have a 85 Y pipe on my engine run stand,, and I should have looked at that b 4 commenting...Duh.
1. Air pump r/h diverter valve bad? remember the diverter valve is
supposed to open to the exhaust when cold, then divert to the cat
when warmed up? could point to a vacuum leak? no control pressure?
could be working on the left, but not on the right?
plugged up R/H check valve, or failed check valve
2. Fuel.....unlikely, but possible,
fuel rail restriction
fuel rail transfer tube clogged
fuel pressure regulator problem
restricted fuel return line back at the tank
fuel pump pick-up screen clogged
3. Electrical.......
broken wire on diverter valve
Bad temp switch in the front of the manifold? Engine stays in
cold open loop all of the time?
leaking cold start valve (on the left side)
cold start valve temp switch stuck in enrichment
4. anybody's guess
Thread Starter
Racer
Joined: Sep 2003
Posts: 322
Likes: 0
From: Gap PA
Thanks RRT, but can you be more specific?
What terminals are you refering too?
The light won't say "code 12", but should flash to show me it, am I wrong?
Thank
Last edited by 85RIT; Jan 14, 2007 at 01:25 PM.
Pro
Joined: Nov 2006
Posts: 638
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From: Plano TX