Sometimes runs great, sometimes not
Thread Starter
Heel & Toe
Joined: Oct 2005
Posts: 20
Likes: 0
Sometimes runs great, sometimes not
I have a 1985 vette that I bought about a year and a half ago. It didn't run when I bought and I was told that it had some problems when he had last drove it (it sat for about a year before I bought it).
The first problem I found was a huge vacuum leak at the runner to intake manifold gasket (It had a lingenfelter superram plenum and runner with a 58mm throttle body). Basically I am just looking for stock performance so I removed the lingenfelter and replaced it with the stock plenum and runners.
It still didn't run very well so I asked some folks what I should try next. I was told that the 58mm throttle body was overkill for the stock plenum so I replaced it with a stock TB. It seemed to run better but still had a problem.
The problem is that at low RPM it will not idle smoothly and when I apply a little gas pedal it will bog and sometimes stall. I figured it was either a fuel problem or a spark problem. I set out to replace each component of both until I solved the problem. I replaced everything (plugs, wires, cap, rotor, coil, ignition module, fuel pump, fuel filter, fuel pressure regulator, EGR valve, TPS, etc.).
The problem is still there. One thing I noticed was that everytime I replaced something, the car would run good for a while. I then figured out that the problem could be corrected by disconnecting the negative battery cable. I then assumed that the problem was with the ECM. I replaced that but the problem still exists.
When I disconnect and then reconnect the battery, the problem seems to clear itself and the car runs great until I shut it off and restart it at a later time when it again will not run at low RPM. Any guess what it is?
The first problem I found was a huge vacuum leak at the runner to intake manifold gasket (It had a lingenfelter superram plenum and runner with a 58mm throttle body). Basically I am just looking for stock performance so I removed the lingenfelter and replaced it with the stock plenum and runners.
It still didn't run very well so I asked some folks what I should try next. I was told that the 58mm throttle body was overkill for the stock plenum so I replaced it with a stock TB. It seemed to run better but still had a problem.
The problem is that at low RPM it will not idle smoothly and when I apply a little gas pedal it will bog and sometimes stall. I figured it was either a fuel problem or a spark problem. I set out to replace each component of both until I solved the problem. I replaced everything (plugs, wires, cap, rotor, coil, ignition module, fuel pump, fuel filter, fuel pressure regulator, EGR valve, TPS, etc.).
The problem is still there. One thing I noticed was that everytime I replaced something, the car would run good for a while. I then figured out that the problem could be corrected by disconnecting the negative battery cable. I then assumed that the problem was with the ECM. I replaced that but the problem still exists.
When I disconnect and then reconnect the battery, the problem seems to clear itself and the car runs great until I shut it off and restart it at a later time when it again will not run at low RPM. Any guess what it is?
Burning Brakes
Joined: Aug 2005
Posts: 772
Likes: 6
From: Huntsville AL
1. The reason it is running good when you disconnect the battery is because the computer is going into default mode. Fuel economy is affected but everything is set to nominal until it relearns your car.
2. Since you have changed about everything else - check:
Timing
o2 sensors - clean and no computer codes
fuel injectors - clean and operating properly
2. Since you have changed about everything else - check:
Timing
o2 sensors - clean and no computer codes
fuel injectors - clean and operating properly
Thread Starter
Heel & Toe
Joined: Oct 2005
Posts: 20
Likes: 0
No codes for O2 sensors and the fuel injectors are new (Forgot to list that on my first posting). Timing is correct.
I did find some information about a couple of recalls for 85 vettes that may be contributing to the problem. I am going to take it to the dealer to see if one of them might be the problem. One is a problem with the coil and the other is a problem with the MAF sensor. I'll report what happens.
Mtrhd329, you may want to do a search online for 87 vette recalls.
I did find some information about a couple of recalls for 85 vettes that may be contributing to the problem. I am going to take it to the dealer to see if one of them might be the problem. One is a problem with the coil and the other is a problem with the MAF sensor. I'll report what happens.
Mtrhd329, you may want to do a search online for 87 vette recalls.
