82 crossfire Corvette idles 1800 won't accelerate or slow down What is my problem?

Answer 1

Before I begin troubleshooting your fast idling problem, I need to know something first. Was your car running just fine before this fast idling problem started? Did the problem start suddenly, or slowly get worse over a period of time? Has anyone been working on your car recently? If so, what did they do? Has the intake manifold or either of the 2 fuel injectors been removed? Has the distributor been out just before this started? As I have driven my Cross Fire Injected 82 vette for 21 years, I know a great deal about them. What you are describing sounds like a massive vacuum leak. As the 1800 rpm idle speed will neither increase nor decrease, it's very possible an IAC motor (idle air control motor) pintle valve is stuck. Or you have a severely leaking power brake vacuum hose. Or a blown plastic check valve at the upper end of that power brake hose. Or a split vacuum hose at the MAP sensor. Or either one of the 2 one way plastic vacuum check valves at the upper left rear of the engine has blown apart (from a recent backfire). As an engine CANNOT run without air getting into it from somewhere, we'll look at the different places that air can get in. The most obvious place is through the throttles of the fuel injection units. And the other place is ANY vacuum hose attached to your engine. So the first thing to do is check the connection of every vacuum hose on the engine, and also check the 7/32" hose that goes from the right rear of the left fuel injector body to your MAP sensor (mounted high on the left side firewall. As the MAP sensor has a 1/4" diameter ribbed plastic nipple, and the hose going to it is a VERY CHEAP 7/32" diameter hose stretched over it, the hose is VERY prone to splitting at the MAP sensor. As a loss of vacuum at the MAP sensor throws the MAP sensor and computer into a false sense of being stuck in a wide open throttle condition (extremely rich), the engine will run quite fast if the MAP sensor hose is split. It's very wise to replace that cheap MAP sensor hose with a piece of 1/4" fuel hose, as the fuel hose is internally reinforced, oil resistant, and will last forever. To check out the individual IAC motors (screwed into the left front of each fuel injector body), take a 3/4" diameter wad of modelling clay (or something similar) and shove that wad down into the "wedge" shaped air port located in the top/left of the injector body (with a flashlight aimed down into that air port, you can see the tip of the IAC motor pintle valve at the very bottom/front). If your engine immediately slows down to idle speed or less when you plug that wedge shaped hole, then you have located the source of the excessive air getting into your engine. Do this for each of the two fuel injectors. When an IAC motor does fail, it will most likely fail with it's pintle valve in the "withdrawn" (engine start) position; opening up the round hole in the bottom of the wedge shaped hole, and allowing a LOT of air in. The more air in, the faster it will idle (in normal operation, the IAC motor withdraws the pintle valve when you are cranking the engine, then upon firing the engine, the IAC motor pintle valve quickly moves rearward (into the hole) to restrict the air; then constantly making small adjustments from then on for changing idling conditions). Don't forget to check the EGR valve either, as it can also get stuck in a wide open position and allow a huge vacuum leak. Even though it's very rare, the rubber body that your "S" shaped plastic line pushes into can get "gummy" over the years, collapse shut inside, and trap vacuum in the plastic line; holding the EGR valve in an open position. First, try simply removing that black plastic "S" shaped line (with the 90 degree rubber end) from your EGR valve. If no change, take your fingertips and lift up the diaphragm of the EGR valve and note any change in RPM (you can also put a short hose on it and suck the EGR valve open with your mouth). It's very possible a chunk of carbon is stuck in the EGR valve "seat"..........holding the valve slightly open. An engine backfire can momentarily blow the EGR valve open and stick a piece of carbon in the EGR valve's seat. Another good possibility is a hardened and broken 3/8" vacuum hose where your PCV valve hose attaches to the front of your intake manifold. If your hose is the 27 year old original, it's as hard as a rock by now and possibly broken (if someone has leaned on it recently). As it's a fairly large hose, it is a good canditate for being the source of your problem. A very remote possibility is the 3/8" diameter flimsy vacuum hose that goes to your brake light switch under the dash. Used to disengage your cruise control when you touch the brake pedal, the vacuum in that line is relieved when you touch the brake pedal. If you (or anyone else) has been fiddling under the dash on that side lately, it was possibly removed and not put back in place. Any recent backfire could have blown a vacuum hose off. But the hose most often blown off by 82 Vettes is the large one at the left rear of the right fuel injector body. The one that slips onto the smooth 7/32" diameter unribbed nipple very easily. If that one IS blown off, locate a very small "Corbin" clamp somewhere, and secure the hose back on with that. And backfires will easily blow the vacuum check valves apart as well. I had that happen to one of my small ones at the upper left rear of my engine, and as the hoses going to it are quite stiff and "set" in position, the valve halves appeared to be together. But upon close inspection, the guts were blown out of it and the plastic body halves came back together; appearing to be undamaged. These one way vacuum check valves are glued together, and after 27 years of being exposed to engine heat, the glue finally fails and the body halves come apart. I hope this information helps you.........................