85 4+3 99k, Rough engine at idle,city or highway

[imogden]

85 4+3 99k
It use to run not so bad, then I had a tune-up. They replaced the sparkplug wires also. The non-mechanic at the shop cleaned out the TB which I still think is the main cause for all my current problems.

During the tune-up, the mechanic broke off the bottom bolt holding on the TPS, the end still in the TB is flush, cna't remove it. Thought about a replacement, rebuild stightly bored out to 52mm TB, but that's $200+ on ebay and a lot of time r/r it. Then they told me my original TPS was bad and I needed a new one, bought that, same results, rough all the time. The bottom TPS bolt is still missing today.

After sitting most of the time over a couple of years (sat more than driven, like maybe a 1000 miles a year), i took it to another garage. He found out that the gas tank had a lot of water in it. He drained the tank, put fresh gas in it, new fuel filter, but still rough. During all this, I left my gas tank cap at the pump and drove off, thought that was why the tank had water. I put in a dry gas additive for fuel injected engines a couple of times, does not seem to help.

Another oddity that I think is a problem, when I get gas, when removing the cap, it seems a lot of vacuum has built up in the tank and I hear a sucking of air sound (really strong) when removing the cap. That may also be causing the water in the tank when the boot gets clogged and filled up over the bottom of the gas tank lip, the vacuum sucks in the water!

1. Is this vacuum sounding stuff suppose to happen, if not what can be done to correct it?

After another year and wanting to drive the vette more, I took it to someone who recommended anothr mechanic, he also did a tune-up. He said the timeing was off alot. Said I might need wires again. I did not have him replace them.

Today, it runs better than it has in the past few years, but under throttle pressure (other than the pressure to just cruise) the engine stutters almost like a cyclinder is missing, but let up on the throttle and maintain speed, it's as smooth as silk.

Love the car, looks great from a distance. I am second owner, 3months old when I get it, have had many many great times with driving and enjoy the moments.

Has anyone else had a similar problem?

Thanks for reading.

Bob

 

[vette-dude]

The whoosh when removing the cap is normal. Sounds like your Throttle Position Sensor (TPS) is not set correctly. The TPS has to be adjusted using a digital voltmeter. I am not sure of the procedure but if you do a search on the toolbar for TPS you will get all the info you need. If the bolt is broke off on the bottom maybe it is moving around and causing the problem. Can't you drill it out and helicoil it? Just some random thoughts.

Randy

 

[AdvancedAutoCC]

Do it right, and find somebody COMPETENT!

You can drill/tap/Heli-Coil the throttle body or get a replacement (recommended). The TPS needs to be mounted properly, but it won't cause a misfire.
First thing is a good visual inspection - look for cracked/broken/missing vacuum hoses. Make sure the plug wires are all on tight (pay particular attention to the #8 wire by the A/C housing).
Next thing would be a complete fuel system cleaning (with a Motorvac, preferably), after flushing the fuel tank again (not just a drain 'n fill). Nowhere did I see anything about the injectors being cleaned (no, "dry-gas" isn't cleaning them), so that's one of the first places I'd look for trouble. Letting it sit around for a year at a time with the same gas in it is not the best course of action.
Finally, make certain that the ignition system is in shape... this includes the sparkplugs, wires, cap, rotor, and coil (does it have the metal ground strap inside the cap, or is it missing?). Are the plugs clean and properly tightened?

Start with the basics before attacking the OBD system (hint - they almost NEVER cause a misfire, but plenty of time/money is wasted chasing ghosts there). If you can't do the job yourself, ask around and find where Corvette people take theirs for care... Jumping from mechanic to mechanic isn't a good idea, and you'll typically waste a lot of time and money.

If you want to do it yourself, buy a Helms manual along with the necessary tools and give it a go... you may find satisfaction in fixing it yourself.

 

[nyernga]

A couple of things come to mind right off the bat. 1) an air leak at the TB where the bolt snapped off........2) What type of TB cleaner did he use? If he used regular carb cleaner then I'd stay away from him in the future...3) I can send you the steps for setting the TPS but if the bottom bolt is missing then everytime you hit the accelerator, you're moving it anyway and adjusting will become a daily thing....4) Advance is right......check all the plug wires with special attention to the #8. If it's not securely fastened it'll pop off and on the surface LOOK like it's connected.
Definately do the basics before spending more money. You'd be suprised how a little diagnosis goes along way. And if you must use a mechanic, post here what he says is needed just to make sure you're not being conned. It DOES happen when they see a Corvette pulling in.

Keep us posted.....

Len

 

[imogden]

Thank you to everyone that has responded, very much appreciated.

I will visually check the vac hoses, then the #8 wire, the TPS adjustment (although it does not appear to be moving), then replace sparkplug wires as a start.

I will update as I complete these.

Thanks again,
Bob

 

[Striker 85]

Get a Haynes manual. That is the 1st step by far. I had similar problems after I had some engine work done. My car would rough idle and die at a stop. After spending more time at the shop then on the road, the mechanic told me he cleaned the TB several time, but I still had the problem. I picked up a Haynes and started myself. Your problem is air intake I bet. It will be at the broken bolt. Also check your air intake for cracks. That was my problem. I dropped an Air Rammer on and the rough idle went away. If you are replacing wires and plugs, go with Taylor 8mm high performance wires and Rapid Fire plugs gapped at .050. You will notice the difference right away in a smoother ride and quicker pick-up.

 

[I_R_DA_ONE]

With that many miles on the car,,,,, I would also check the injectors---this can be done by checking the resistance of each one ... if the resistance is lower than 10 ohms I would replace it..
Mike R