I have a 2005 chevy colorado 4cylinder, 5 speed manual, 58K miles, and I have had a recurring problem with an erratic idle. The problem occurs usually when I am coasting with the clutch in or in neutral, which I normally do when coming to a stop. The RPM's will drop as they normally should when not applying any throttle, but they continue to drop below 500 rpms, which causes the truck to shudder. The RPM's usually "bounce" back up to normal and then drop down low again.
The first time this happened was about a month after I had bought it and the truck had around 50K miles. The problem happened infrequently at first and I didn't think much of it until it got worse. Soon the engine light came on and I got the trouble code for a communication error between the crankshaft position sensor and the camshaft position sensor. I replaced the camshaft sensor and wiggled some wires around but the problem persisted. The crankshaft position sensor is not available to purchase yet and so I brought the truck in to the shop. They said that I had a major misfire but they didn't know why. They reset the computer and the truck ran fine. I got off light paying only $125.
The problem returned in 2 months gradually but got worse much faster and this time the truck stalled a few times when I started it and the check engine light was back on. I managed to get it on the road and I got a trouble signal that said that I had "reduced power" but I managed to make it to the local Chevy dealer (less than a mile away).
This shop said that it was the "crankshaft solenoid" which I didn't know existed, and they charged me $300 for the job. The truck was fine for a few more weeks.
Now the problem occurs on occasion but has not yet gotten too bad. The engine light has not come back on either, but I don't want to wait too long for it to come back.
Does anyone have any ideas for me? I don't want to sink any more money into this problem and I do consider myself to be mechanically inclined, but I am stumped on this one.
