Cold Start Idle Question

WRGoudy

Registered User
I've read through and searched most of the posts on the board and haven't found the answer to a problem I'm having, and thought it can't hurt to ask for help. I bought a '91 SC last fall, and immediately did a major tune-up (wires, plugs, all fluids/filters/etc., replaced leaking intake gaskets, vaccum hoses, and some other things I can't think of at the moment) after which the car ran simply perfectly for a stocker.

I've recently started having problems that seemed to start when the weather turned really cold (sub freezing to single digits)where-in the car will start right up with no problem, idle around 1200rpm for maybe five seconds, and then try to fall on its' face and die if I don't play with the throttle to keep it running. It runs fine once under way as long as you apply at least a little throttle, but will still idle very low (=<500rpm) or die at a stop unless you stay on the gas a little.

Once water temperature gets up to about 140-165 degrees (according to the mechanical gauge I'd installed), it idles fine and the problem disappears. Since the problem only happens when it's cold outside and the motors cold, I'm thinking it's probably the Air Charge Sensor, which according to the Haynes manual (suggestions for a good manual?) I have sends a signal to the EEC to correct/control fuel for cold start enrichment (I read as a choke equivalent).

Any input would be appreciated. Oh yeah, I'm not getting any check engine lights or 'yellow" arrows at any time for what it's worth. I'll probably check codes tomorrow at the shop, but thought it would be worth asking for input from the more knowledgeable board members in the mean time.

Thanks in advance.
 
ACT Sensor

Well I changed the Air Charge Temperature sensor and while it might be slightly improved, still pretty much acting the same for anyone that's interested.

Still looking for the answer to this problem if anyone has any ideas.

Thanks
 
vacum leak

The clue is the work you did. Somwhow, somwhere something did not seal up 100% and the system is very senstive to this when warming up (open loop mode). For me, it was a loose spanner nut.
 
maybe

the IAC valve ...is icing up .once... it kicks off high idle...and engine heat frees it up.. after it warms up ... winter thing ...if it's only happening ..when really cold ..could could try to apply a little heat to the thottle body ..before it stalls to try and trouble shoot it ..... dave
 
or not

If the IAC were non-functional, you would not get a high cold idle for starters. And if it iced up on start up, you would be stuck on high idle until it warmed up and melted.
 
MrNiftie Wins this round

Well it works fine now.

After work last night I was poking around under the hood - checked codes and got a TPS voltage high (.96v) and one to do with a fuel pump voltage missing somewhere the computer expected to see it if I remember properly - I forget the numbers but have them written in the book that's at the shop.

While there I checked the spanner nut at the SC and could turn it by hand - not a good sign. I had used a GoreTex (sp?) teflon sealing tape that I got from a power plant job I was on a few years ago to seal all IC piping, and since it's relatively pliable (about 1/2" wide by 3/16" thick before compressed) apparently it had too much give for this application. The stuff is rated full vacuum to I think 3000 psi, and something like minus 50 degrees to +550 or so.

I used a good quality strap werench to tighten the spanner to the max, and a drift and hammer to determine that it wouldn't go any tighter without using the proper spanner that I don't have. Also retourqed all other piping connection nuts.

This morning, probably about 20 degrees outside, the motor started and idled just fine. I had read many posts regarding checking for vacuum leaks and obviously they were correct that this should be the first thing to check. I'm now getting 19-20" of vacuum at idle which is up at least 3-5" from before.

Guess I'll order me up a set of those reusable gaskets I've seen mentioned several times here (from TBird88? if memory serves


Based on what I read here elsewhere last night, the TPS voltage should be about .94v so I suspect the scaner software may be incorrect? I know that something closer to .75v is more common for most vehicles, but assume as with many things SC related, this ones a little different.

I'm not too concerned with the other code relating to fuel pump voltage as the car now runs extremely fine again.

I thank everyone that responded to my help request, and based on some of the other posts I read for this exact same issue, can only say - check for vacuum leaks. Was going the propane route next, but since the spanner was only hand tight didn't bother. Will probably still try that once it gets a little warmer here.

Thanks again all.
 
Glad to help!

After taking a long siesta, I'm getting back into things again! Ideally, the voltage should be as close to 1v without going over. 0.9 something is good. As I recall, to tweak it, you have to elongate the holes of the housing slightly (filing) so that you can rotate the sensor a bit to fine tune it's position. Stock, it's non-adjustable.
 
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