Ok, this is a little weird and scary. Here’s the problem I’m seeing of late:

(original stock Q-Jet)

-car has sat outside overnight, or has sat for a few days in garage
-normal cold-start procedure
-press and release throttle pedal to floor once or twice to set choke and squirt some fuel
-start cranking
-often, the engine ‘seems’ to fire instantly (less than 1 second), so I let off cranking but the engine never actually starts
-so I start cranking again
-if after 3-5 seconds and no sign of the engine firing, I gently add about 25% throttle

After this point the engine will often fire up normally. However, the fast idle usually does not kick in so I hold the throttle and let the engine run at 1000 rpm for 1 minute to warm things up before driving. Warm and hot starts are completely trouble free; car fires up instantly.

But lately I’ve experienced this during cold starts:
-cranking for 5-10 seconds, sometimes modulating the throttle
-the engine will fire up and sometimes sputter for 1-2 seconds, and then ROAR, it goes to straight to redline!!!

My foot is completely off the pedal! So I either immediately cut the ignition or sometimes stomp on the pedal to get it to come back down to normal idle.

As you can tell, this is really scary and dangerous, and especially hard on the engine when the oil is thick and cold. The frequency of this is increasing as it used to only occur once every few months. Now I'm scared to start my car because it happened 3 times last week.

So what the hell is going on???

Obvious things:

The primary throttle shafts have nice smooth movement by hand and the cable and linkage do not bind or get stuck. I’ve never experienced a stuck throttle under any driving circumstances. All return springs are in good shape. Both primary and secondary throttle plates snap shut.

When it happened this morning, just after I cut the ignition I had a look and noticed the throttle stop was touching the idle adjustment screw so I know the primaries were not stuck open or even engaged at fast idle. The choke plate was at about 50% closed. When I did get it finally started, there was a small backfire out the pipe, which I’ve never had before.

How can an engine go to WOT without air? It can’t right? …so somehow extra air is getting in and causing this. I suspect the choke linkage but I can’t see how it could occasionally jam the primaries wide open?? Should I be looking at the secondaries or the air valve as well?

 

have you tried starting the car with air cleaner and base removed? My first thought would be throttle cable/ linkage is getting stuck somewhere.... have you changed ANYTHING under the hood recently?

re-read your description, and I notice that your cold start procedure involves flooring the gas pedal to set choke and feed in some gas. (I do the same thing) That also could be where the throttle gets stuck open?

 

I concur with above however take it one more step.Take a friend with you and remove air cleaner.have him press acc pedal to floor but do not crank car .After he lets up on pedal observe position of throttle plates to see thier position .A common problem on qjets is wear on the housing and throttle plates can stick..If this is the problem the housing can be drilled and new bushings installed.Step 2 . remove carb .Send to Lars .Have him rebuild. reinstall .Big smiles.

 

Just a thought ....

Maybe your idle stop solenoid is messed up and the plunger is extending all the way out ...

I know on my 72' that the idle is actually set by adjusting the plunger on the idle stop . If I leave the key on for several seconds then try starting, the idle will kick up to 1300 rpm, then settle right down to 800 rpm.

Im not sure what year and engine size your car is - but the TCS system and the idle stop are linked together - and sometimes can act funny ....

Hope this helps some.

Bill

 

i haven't messed with anything lately. performance and driveability have been good all along.


i did install new bushings on the throttle shafts years ago.

good suggestion, i will get someone to watch what is happening under the hood during each step. my g/f would love to watch the little thingy attached to the other little thingy... hehe. i guess i'll get my brother over


engine is stock 454 in 72 4-speed. TSC is long gone


good idears all

 

wondering if i should try to completely remove or bypass the choke mechanism to see if the problem goes away. i shouldn't need it for rest of summer... i hope

 

I had another thought (which is a topic title in itself!! ) but I was making my own carb spacer a while back and when I test fitted it I realized the tolerances down there were extremely close, in other words, my home made spacer was likely going to catch on the plates down there. I would also check to make sure your gasket hasnt slipped or otherwise the flapdoodles (the round plates that flip open when you tromp on the gas) aren't sticking open.

 

My car started doing the same thing last year. It is definitely a scary thing, and I could get it to not rev if I hammered the gas pedal right when it happened.

I thought it may be the return spring, but it didn't happen all the time, so after one time that it happened. I pulled the air cleaner and had a look inside the carb. I noticed that the "flapdoodles" (LOL!) inside the secondaries were cracked open just a little bit. I was able to carefully close them with a screwdriver, then it would start normally.

After discovering this, I noticed that the car never revved up on starting if I took the car out for a leisurely cruise - probably not opening the secondaries, so they did not have a chance to get stuck open.

My solution is sitting in a box, waiting to be installed - a correct numbered carb. I was planning on doing this anyway. The old carb is probably just tired and needs a rebuild.

 

also make sure it's not bleeding off gas out of the bowl after a few day's