idle on Hotside

[joemc]

It's been awhile since I have driven my Miata. The battery was diconnected all winter and Spring. I have a battery tender to maintain the battery.

When I come to a complete stop - the idle is about 1500 rpm . approx 20 seconds it will drop to 1100 rpm and 10 seconds later drop to 800 rpm.

If I am going down the road (long hill) and put the clutch in it will maintain the idle at 1500.

Wonder what I need to do to adjust this? don't want to get a high speed CEL to come on

[FormerDatsun510Man]

Does your Hotside have an Air/Air Intercooler? If so, having a high idle is the nature of the beast in order to avoid idle dip or idle stall (especially with the A/C on). I recall on my Air/Air Intercooled Hotside I got the best results by setting the idle with the jumper between the ground and ten terminals to 1100rpm. This would cause it to hang for a minimum amount of time at high idle before dropping to about 900-950rpm or so, and yet not stall. The stock idle is 850rpm.

If you have a Hotside without an Air/Air Intercooler (either non-intercooled or with an Air/Water Intercooler), then you can set the idle the more proper way with the ground and ten jumpered at 850rpm.

One final note, I found that if you disconnect the battery long enough so that the factory ECU is reset, the idle will be higher than where it will eventually settle after a few days of driving. This is especially the case when you have to set the idle higher for the aforementioned Hotside with Air/Air Intercooler. Also, as far as a CEL goes, I found that as long as you keep the idle at 950rpm or lower (once it settles), you shouldn't get a CEL for high idle.

Bill

[joemc]

I have the A/W intercooler.

Idle droop has always been a problem even before the SC install. I have just over 25K miles and every year I have to remove and clean the throttle plates.

Just has to be a poor design by Mazda

[FormerDatsun510Man]

When I bought my '00 Miata new off the showroom floor, it developed a slight amount of idle dip when stock. I simply turned the idle air screw counterclockwise about a 1/2 turn and it idled fine again. On your Hotside I suggest you first drive it a few days for the ECU to settle the idle a bit more and then if it is still hanging at a high idle adjust the idle down a little bit at a time until the idle hang disappears. If this then introduces a little bit of idle dip, it isn't anything to worry about unless you find that it drops down to say, 500rpm or lower. If excessive idle dip or idle stall occurs, then you need to go the other direction and turn the idle up a little bit at a time. Be sure to check this condition with the AC on. On Hotsides I found they need to be adjusted for the idle on the high side (900-950rpm) to find that balancing point and yet still avoid the CEL. The good news is with your setup running an A/W IC, this condition is minimized.

The Coldside is an even better solution :biggrin: j/k

Bill

[joemc]

Decided to waste my money on a new furnace and air conditioner for the house instead. The contractor was amazed I was still useing the original one from 1960 when the house was built. But the way my house is designed I can't get a 95% one where there is a tax credit. :(

appreciate the suggestions. it would drop below 500 and stall unless I tapped the pedal a wee bit at the stop. that's when I knew it was time to clean the plates