CaseyJones

This is an issue I've had for years on different vehicles and I'm tired of dealing with it on my 80.

I'm running a 350 with 10.5 to 1 compression and a Comp 268H cam. I have the stock Q-jet on a Performer intake and an aftermarket factory replacement hi-perf distributor. It has slightly reworked L-82 heads, Hooker long tubes and true duals. I still have the 350TH tranny with a shift kit.

The car idles fine at around 850-900 RPM depending on the air/engine temp. When I drop it in gear the idle drops to 650-700 but still feels good. When I put it in park, the idle jumps up to close to 1200 RPM but drops back to "normal" after a few seconds or a couple of light taps on the accelerator. Yes, I have new return springs.

Off-idle performance is acceptable but a tad sluggish until I hit 1200-1400 RPM and then it pulls great. Around town driving is good and highway performance is terrific. Gas mileage is very acceptable. My vacuum system is in good shape with all new hoses, actuators, relays, etc.

Is there anything I can do to decrease the hot idle speed in Park without having it stall out in Drive? It sounds like the motor is racing in Park and the RPM drop into Drive seems excessive. Everything seems to be adjusted right, but I'm missing something for sure.

Questions, comments, and cheap shots welcome.

johnt365

I would adjust the choke wide open to rule out any possibility of a choke high idle issue.

What converter do you have? What rear gears do you have?

I have a comp xe268h cam and 3.55 gears and with a 2800 converter , I could get it to idle right at 600 or so rpms and there would be no change when put in drive. If I recall, it would just barely start to roll back on a slight hill.

Perhaps a different converter may get you in your power band quicker and help the idle in gear.

76Vett

I have the same cam XE268H, idles at 650 and very good off idle performance. I do have 3.70 gear with a 200R4 trans/2400 converter - that makes a big difference.

Ironcross

this will help cure your problems........

oldschoolvette

I agree check the choke as well

REELAV8R

What is your initial timing set at? This sounds like retarded timing. Initial should be around 14* to 16* for that cam.

Check your mechanical timing advance. It can get sticky due to old oil/grease then does not readily return to the fully retracted position. And it may act fine when cold but become sticky when hot, I chased that gremlin for a while. You should be able to twist it and it should snap freely back to fully retracted position.
Your symptoms seem to point to the carb, but I suspect they are timing related.

MelWff

In addition to what REELAV8R stated are you running the vacuum advance to manifold vacuum? The extra advance from that will help with your idle issue.

CaseyJones

Very curious about a replacement converter. I assume that a 2400 would be enough. since my lockup hasn't worked in some time but the tranny still shifts fine, do you have recommendations about brands and such?

lars

Your converter has nothing to do with your idle speed issue. If you want a different converter, that's fine, but it won't solve your idle speed problem.

You have a timing problem where your timing is changing between the rpm and vacuum you're pulling in "drive" versus "park." If you're running manifold vacuum to your vacuum advance, you have to have a vacuum advance control unit that pulls in its full advance range at a level 2" numerically lower than the vacuum reading you're getting in "drive." You also need to be running centrifugal advance springs that do not alter the advance between the "drive" and "park" rpm difference. Once you obtain a steady and unaltered timing advance at both "drive" and "park," your rpm difference between the two will be normal. You can e-mail me for my timing papers addressing these issues.

Lars
V8FastCars@msn.com