Hey everyone, The idle on my 5th gen is odd, and I wonder if it's a common problem. I would expect that a normal idle would be somewhere between 1100 - 1200 rpm. However, when I start it up, idle is a little high, at about 2000. I could live with that, but at about 160 degrees it jumps to nearly 3000, then it drops back down to 2200 or so when it hits 185 degrees and runs at that idle until it cools back down. Does this wacky speeding up when its warm sound familiar to anyone, and how do I get it to behave more "normally" from a cold start? Thanks for any guidance. Jose
If your 5G is from 2000 or later, there is a fast idle device built into the throttle bodies called a Wax Unit. This has coolant flowing to/from it so it is exposed to the temperature of the engine as it warms. Basically when cold the wax unit contracts and pulls the starter valves open for a fast idle, as the coolant heats it expands and lets the starter valves rest on the idle adjuster screw. First up I'd suggest you make sure you have a good flow of coolant as the hoses are tiny and can get blocked. After that check the wax unit is expanding and contracting to move the starter valve plate, and the SV plate rests solidly on the idle adjuster when the engine is warmed up (my guess would be 120F or near offer) with a little slack from the wax unit. Probably not impossible for the wax unit to fail internally so if it is not moving as expected when there is a known good flow of coolant then it may need to be replaced. Some have also adjusted the nut on the wax unit shaft to change the engagement with the starter valve plate. 5G's from 98 and 99 don't have wax units, fast idle is controlled from a bar-operated lever like a choke lever for carbs. One other possibility would be an air leak into the throttle bodies, so it would pay to check the vacuum hoses used to synchronise the vacuum are all in good, un-cracked and plugged in state.
Fantastic information, Terry. I do have a 2000. Maybe it has some weird partial failure condition, that prevents it from opening totally cold, but allows it to kick in when temp hits 160. I would expect an air leak to be constant, but I suppose it could cycle with heat. I'll give it a test with some starter fluid or propane. Cheers.
My 01 had been sitting for a long time when I bought it, and it was left with air in the cooling system. The WAX unit hose is at the very top of the thermostat housing and has a very small internal diameter, air will accumulate there if partially full. This in turn causes corrosion as well as coolant drying and going hard, this will block the pipe and WAX unit, at least that's how mine was and had the same fast idle problem. The down side is you have to remove the throttle bodies to get to it. So as Terry suggested, I would check for vacuum leaks first as this will cause the same problem. If you do remove TBs, I recommend replacing the thermostat and O rings. And don't panic about removing them, it's not as bad as people make out, it takes me around 30 minutes to have them off but it is a bit of a pain to get them back in. Good luck.
