Poor idleing at High Altitude
 

This is my 1st post to the forum. Thanks for reading.

I recently purchased my dream car. '83 911SC Targa.

Idle was perfect when driving in California, but the lack of O2 in my Colorado mountain town (9,000 ft) has the car searching for the correct idle, and trying to die at stop signs on occasion.

I've been hoping that, over time, the car's sensors would 'learn' the correct mixture, and fix itself, but that hasn't happened to my satisfaction.

I'm looking for suggestions/info before bringing the vehicle to a mechanic, so that I don't go in there seemingly ignorant about the probable remedies.

Thank again.

-KVH

I've seen cars with motronic with it's map sensor, throttle position sensor, and oxygen sensor have that problem being way too rich at 9000 feet above sea level too.
Maybe the o2 sensor was used up.

At those altitudes a turbo is great... makes up for the lack of air up there.

should be able to adjust the mixture at a shop to fix the issue.

KVH,

Congratulations on the new ride! You will without a doubt need to adjust your base settings for fuel- your car cannot "learn" like the late cars. Typically what we see in Denver- a car setup for near sea-level operation runs at least twice as rich as needed when it arrives here - depending on engine health/exhaust modifications/state of tune/fuel quality/etc. etc. Your O2 sensor can't pull enough fuel away to run correctly without getting the idle mixture set correctly first.

Best,
Orrin

KVH,

Theoretically CIS is supposed to compensate for altitude. It doesn’t.

You will want to get it adjusted for your altitude. Depending on where you are, there are some great shops that can get you the best possible.

You also may find it easier for you to get the tools and DIY. There are some mountain communities with mechanics who claim expertise but ….

Here in Denver, Orrin is one of the good guys to see. If you set the mixture here in Denver (5280’), it will be very close for 9000’.


Be sure to have (or know how to) get the mixture set back to sea level specs BEFORE you go back down to low altitude. Damage can result otherwise.

Best,
Grady

Unfortunately CIS has no adaptive learning strategies like today's modern cars, nor can it compensate for altitude without human intervention.

Looks like I need to start by getting a pro to adjust.

Thanks for the info!