Chevy Caprice Classic - Rough Idle, Dies in Gear

Scan the "New" computer for trouble codes.

yes and even though the NEEDS COOLANT LIGHT still remains on no diagnostic codes come up

sounds like a bad ground. Your injectors in the throttle body are controlled by the computer. The computer makes and breaks a ground to the injectors. There are three grounds you should clean the terminals on 1 is under the bolt which holds down your thermostat housing 2 is a big braided wire from the block to the frame 3 is on the back of the passenger side cylinder head. you can also check this by taking a razor blade and just penetrate the plastic coating on the black wire going to your injector, with the ignition key to the on position touch the razor to the side of the throttle body housing (while in contact with the black wire) you should hear a click and be able to see that injector shoot fuel into the intake.

Just a thought, fuel pump? After the car has been off for an hour or so, with all accessories turned off, turn the ignition switch to on, not start. You should hear the fuel pump start when you turn the key. It will stop in 1-2 seconds if it is in proper working order. If it goes longer than that you may need a new one.

(1) Typically, low coolant light is connected to a switch in the radiator. It is typically not an input to the ECM (Electronic Control Module).

(2) Why was the computer "board" replaced? (Are you referring to the ECM, or the PROM in the computer case?) Also, why was the O2 sensor replaced?

(3) You should check fuel pressure. You can tap into the line at the filter (inline gauge adaptor to temporarily replace the filter) or into the line at the TBI.

(4) Pressure regulator spring in the TBI does have a known problem with breakage. This will (sometimes) cause the symptoms you describe.

(5) Disconnect (carefully! shut engine down, then disconnect one at a time) the connectors to the TBI and see if the performance changes. You also should attach a "noid light" to see if the ECM is pulsing the injectors.

(6) EGR passages in the intake can be plugged up. Pull the valve to check for carbon buildup. Also, the valve itself can hang open from carbon buildup. Check when you pull the valve.

(7) Have you attached a scan tool to check for your codes, or are just jumping the A-B connector to get a flashing CE light? If not, I would suggest doing so to see what the data stream looks like.

Let us know your progress, if you please.

Check the throttle position sensor. Small black box on left side that has a wipe arm hooked to the throttle. If I remember corectly it should be 4.5-5 volts at idle and should increase in voltage as throttle is actuated. Hope this helps. There is also an Idle Air Control Motor but I'd do TPS first.

I am being nickeled and dimed to death on this one.

Another approach, get schematic and pollution control device diagram. Then one at a time check each sensor/pot; apply ground jumper until apparent change ocurs when you disconnect.

I'm partial to Moore's suggestion due to an experience where I overlooked grounding of a motorcycle engine, and suffered intermittent run.

I also got a huge bill from my mechanic for my truck (Cargostar International) -not a pickup, because the last thing they considered was the wiring harness, which had over time cracked apart due to the way the cablift, to expose the engine was designed.

(Cab pivots back stressing wiring harness.)

Guys who turn wrenches do not necessarily notice electrical problems, is part of my experience, and your statement that you are being nickeled and dimed inclines me to think well of Moore's suggestion.

I had an old Mustang 5L (TBI) with a similar problem. In my case it was only a bad fuel pump. Idle to maybe 15 mph possible, then stall. Pump "whine" in tank had been getting louder. Replaced pump and it ran fine. Good luck!

As an old wrench turner, might I suggest also to check all vacuum lines?

The symptoms you decribe do point to a fuel/air mixture problem.

Another clue: smell your exhaust while it is running......

Like changing the choke control from winter to summer or replacing a faulty EGR or vacuum modulator valve to the tranny.

I want to thank each and everyone of you for taking the time to send me your input I'm going to start at the top and work my way down and I most certainly will let you know the outcome. To answer the question why was the oxygen sensor replaced and the computer board I was told that after dianostic testing it indicated they needed replacing. No codes are reading now just the Low Coolent Light remaims on and once in a while the Service Engine Soon light. I sure wish I still had my 72 El Camino at least back then things were alot less headache and alot less TOOLS!! Wish me luck here I go ..

Sounds like a vacuum leak.

I had an old Pontiac that ran that way. Problem was bad fuel injectors. Replaced 5 of them (out of 8) and car ran well after that.

Try to keep it simple with this old small block. You don't have that much state of the art technology on it. Remember your basics you have to be sound mechanically before anything else will work properly. Validate your warning lights. Does it really have a low coolant level, why? Investigate that. Service engine soon lights for this vintage are not the same as check engine lights. This was a mileage driven warning usually linked to recommended EGR valve replacement. If you want to talk about a vacuum leak that will make it hard to start and keep running you couldn't find a bigger one.

Your TBI is still not much more than a glorified carburetor. The system works from a set of fixed instructions when cold and in open loop. It can not respond well to a wide range of variables.

On a final mechanical note once upon a time "soft cams" would occasionally show up on older 5.7's if you depended entirely on scanners you would get all kinds of crazy codes and spend a lot of money needlessly. It all goes back to the basics.