Quadrajet Problem Solving > Diagnose a Quadrajet carburetor problem

TPS/O2 Sensor Codes

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jameskuzman:
Hi all -

I posted a few days ago about a hard-stating-when-warm problem with my '85 LeSabre after rebuilding the carb (E4MC).

Since then, the SES (Service Engine Soon) light has come on, and in addition to the warm start problems, it's taken to idling too fast when warm.

I pulled the codes tonight at got a 22 (TPS Voltage Low) and a 45 (O2 Sensor - Rich Exhaust).

Would a bad TPS cause the high idle, rich exhaust, and/or no-start problems?

I'm going to replace it regardless, I think, but was just curious to know if it might be the cause of all of the symptoms.

Thanks much,

Jim

Cliff Ruggles:
The TPS has no control over fast idle when cold, curb idle speed when hot,  or how well the engine starts.

If you are having cold start issues, check the choke and the accellerator pump, and make sure they bowl isn't dry from leaking bottom plugs.

The choke pull-off unloads the choke flap on cold starts, and the fast idle speed is controlled by the adjustment screw on the passengers side of the carb under the choke housing.......Cliff 

jameskuzman:
Thanks Cliff!

Cold starting is actually ok now.  It sets up on fast idle by opening the throttle a bit (warm down here!), starts well, and runs very smoothly. The choke opens just enough and releases progressively over the course of a minute or two.  No issues there other than the fact that blipping the throttle does not bring it down from the highest step on the cam to second highest.  Fast idle speed does drop down as the choke opens, though.

The real problem is warm starting after the car has been sitting for an hour or so.  It acts as though it's not getting fuel at all.  Reminiscent of the old vapor lock, actually.  If it's only been a few minutes, it fires right up.  Otherwise, it cranks but won't catch.  Doesn't even sound like it's TRYING to catch.  Then, out of the blue, after waiting another hour or so, it fires up as soon as I hit the key...

Thoughts?

Jim

jameskuzman:
Cliff, I should add that the high curb idle is unusual in that the throttle doesn't even contact the tip of the curb idle screw, so there's no way to adjust it down. Wondering if it got bent at some point, but I can't recall any point in the rebuild when that would have happened.

Jim

jameskuzman:
As an update to the thread, I pulled the carb off the car last night and found the bowl was full of fuel after sitting for 3 days - so I think we can say any hard-starting issues are not related to drain back or leakage.

The accelerator pump was squirting fuel when I pressed the plunger, so that's working ok, too.

I'm going to replace the TPS in the next few days because of the code it keeps throwing.

As far as the high curb idle, the throttle is not closing against the adjustment screw even when it's all the way out, and the primary plates are open just under 1/8" when the throttle should be closed.  I can see that it's being kept open by a tab that rests against the fast idle cam on the choke side of the carb.  It's on the lowest step, but that's definately what's keeping the throttle open and causing the high idle. 

Suggestions (other than bending this tab, unless that's what you're really supposed to do) on getting the throttle to close all the way are welcome.

Ditto any thoughts on what's causing the no-start condition after the vehicle has been sitting an hour or so. 

This was NOT a problem before the rebuild, so I immediately looked to something I did wrong with the carb first, but I'm wondering if that's a red herring and the problem is coincidental and possibly electrical in nature....?

Thanks to all,

Jim

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