85 idle creep (stock distributor)
Thread Starter
4th Gear
Joined: Jan 2026
Posts: 4
Likes: 0
85 idle creep (stock distributor)
I have an 85 that was carb swapped when I bought it, it was kind of a hack job so Ive been slowly doing everything right. Ill preface with everything it has in it.
Brawler 750 race carb
NA Holley manifold (I dont remember off the top of my head)
and the stock distributor
Timing set to 10° btdc at idle
My first guess is the digital advance is my problem.
On start up it will idle at about 650-700 and then slowly go up to 1300 at that point it will sometimes run off or diesel which hasnt been a problem lately since fixing the fuel pressure and plumbing the pcv port to the brake booster.
Brawler 750 race carb
NA Holley manifold (I dont remember off the top of my head)
and the stock distributor
Timing set to 10° btdc at idle
My first guess is the digital advance is my problem.
On start up it will idle at about 650-700 and then slowly go up to 1300 at that point it will sometimes run off or diesel which hasnt been a problem lately since fixing the fuel pressure and plumbing the pcv port to the brake booster.
Supporting Vendor
Joined: Nov 2025
Posts: 262
Likes: 29
From: Cotopaxi, Colorado
I have an 85 that was carb swapped when I bought it, it was kind of a hack job so Ive been slowly doing everything right. Ill preface with everything it has in it.
Brawler 750 race carb
NA Holley manifold (I dont remember off the top of my head)
and the stock distributor
Timing set to 10° btdc at idle
My first guess is the digital advance is my problem.
On start up it will idle at about 650-700 and then slowly go up to 1300 at that point it will sometimes run off or diesel which hasnt been a problem lately since fixing the fuel pressure and plumbing the pcv port to the brake booster.
Brawler 750 race carb
NA Holley manifold (I dont remember off the top of my head)
and the stock distributor
Timing set to 10° btdc at idle
My first guess is the digital advance is my problem.
On start up it will idle at about 650-700 and then slowly go up to 1300 at that point it will sometimes run off or diesel which hasnt been a problem lately since fixing the fuel pressure and plumbing the pcv port to the brake booster.
have you also check for vacuum leaks at the base of the carb ?
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Melting Slicks
Joined: Jul 2003
Posts: 3,497
Likes: 877
From: Saratoga Springs NY
2024 C4 of the Year Finalist - Modified
2022 C4 of the Year Finalist - Modified
Yeah you cant run the stock distributor. Get a basic HEI with mechanical and vacuum advance and should be set to go. Anything the ECM controlled is no longer gonna work.
Racer
Joined: Sep 2017
Posts: 375
Likes: 89
From: Alaska
X2 on a distributor intended to run with a carburetor.
If you choose to run a large cap HEI choose one with a performance oriented advance curve. OE, "coil in cap" HEIs with a mechanical advance were tuned for emissions with their famously slow and exceptionally long advance curve.
I've heard of as much as 34 degrees of advance and not reaching full advance until after 3,000 RPM.
Accell markets a distributor that supposedly has a performance curve and, possibly an adjustable vacuum advance.
Lots of options, just stay away from the ones that are made to look vintage-ish, with a 4 pin HEI module off to one side under a tin cover. Everyone I know that has tried one of those, had to replace it shortly after installation.
Or, if you can come up with a used HEI for cheap (free) it would be worth it to try, so you can verify it is in fact an ignition issue, just don't drive it with the stock advance curve.
The long advance curve of a smog era mechanical advance could mean once you have enough initial advance to make the engine start and idle correctly, could result in excess advance and possibly detonation further up the rev range.
+1 on TPDO's suggestion of checking for vacuum leaks.
If you choose to run a large cap HEI choose one with a performance oriented advance curve. OE, "coil in cap" HEIs with a mechanical advance were tuned for emissions with their famously slow and exceptionally long advance curve.
I've heard of as much as 34 degrees of advance and not reaching full advance until after 3,000 RPM.
Accell markets a distributor that supposedly has a performance curve and, possibly an adjustable vacuum advance.
Lots of options, just stay away from the ones that are made to look vintage-ish, with a 4 pin HEI module off to one side under a tin cover. Everyone I know that has tried one of those, had to replace it shortly after installation.
Or, if you can come up with a used HEI for cheap (free) it would be worth it to try, so you can verify it is in fact an ignition issue, just don't drive it with the stock advance curve.
The long advance curve of a smog era mechanical advance could mean once you have enough initial advance to make the engine start and idle correctly, could result in excess advance and possibly detonation further up the rev range.
+1 on TPDO's suggestion of checking for vacuum leaks.
Melting Slicks
Joined: Aug 2003
Posts: 3,395
Likes: 393
From: Lakeville MI
The stock distributor could still work with ecm control, however the load value will be a bit contrived.
With no tps and no maf inputs, the load value should run around 100 based upon default tps and the default airflow calculation with both tps and maf failures present. Since the load will be relatively fixed, the spark advance will only really vary with rpm and could be tuned within the limited expected load range. Certainly not ideal, but could be made to work reasonably well much like a mechanical advance. Adding a functional tps would improve things significantly.
The op has not explained if the ecm is still in the loop and if any of the inputs not already discussed are still connected (such as coolant temperature, rpm, etc).
With no tps and no maf inputs, the load value should run around 100 based upon default tps and the default airflow calculation with both tps and maf failures present. Since the load will be relatively fixed, the spark advance will only really vary with rpm and could be tuned within the limited expected load range. Certainly not ideal, but could be made to work reasonably well much like a mechanical advance. Adding a functional tps would improve things significantly.
The op has not explained if the ecm is still in the loop and if any of the inputs not already discussed are still connected (such as coolant temperature, rpm, etc).
