Hesitation when accelerating

[reeder123]

I'm experiencing some hesitation from the engine when I try and accelerate, it's especially bad when I first start the car in the cold. It starts just fine, takes about 5 minutes before it'll feel like it's idling strong and when I pull out of the driveway it pretty much stops dead unless I really give it some gas at pump the rpms to the max which can't be very nice for the neighbors when I leave for work at 5am (and it does this in every gear). Once I've driven for about 10-15 minutes and the engine is nice and warm the hesitation isn't as bad, but I still feel like I'm not getting as much power, just to get up to 60MPH in the highway I have to floor the accelerator and it's killing my gas mileage. I've done some searching around the forum and my conclusion is a vacuum leak, but my question is could it really be a vacuum leak even if it eventually improves once the car is warmed up? As always any insight on the matter would be greatly appreciated!

[dlb]

yup, could def be a vacuum leak. lots of the emissions control system is used to help the engine warm up quicker, like directing exhaust gases to the base of the carb and whatnot. take a look for any disconnected or damaged hoses.

it also sounds like your choke could be stuck open. i had similar symptoms last year when the weather started getting cold. when i pulled the choke mechanism apart, some of the parts were stuck and kept the butterfly valve open all the time. didn't take much force to loosen the stuck parts. i lubed them up with WD40 and it's been fine since.

[Petros]

actually could be another problem, the accelerator pump. A vac leak is a possibility, it leans the mixture so the engine will always feel weak. It is worse when cold because it needs a more rich mixture (fuel does not vaporize as well when cold). So check for vac leaks first by a careful inspection of all the vac lines, and than using a can of carb cleaner, spraying on the various locations with the engine running. When you hit a leak the engine will change speeds. Even if you have another issue the vac leak must be corrected first. And even if you find one do not stop looking, I once bought a Tercel4wd cheap because it ran like crap, I found nine vacuum leaks!

The accelerator pump gives it extra fuel to accelerate the engine rpm (a temp richening of the mixture), this effect will be present both when cold and warm, but not as bad when warm. There are two accelerator pumps on this carb, the main one is driven by the lever on the top of the carb that pushes a plunger down along side the float bowl. The other is the AAP (auxiliary accelerator pump) and is the vacuum operated diaphragm on the left side of the carb. If it is that bad I would say it is the primary accelerator pump.

A quick check is to look down the main barrel of the carb with a flash light and than rapidly advance the throttle (the engine can be off), you should see a strong stream of fuel squirting down the barrel. Not a dribble or short spurt, but a steady stream like the stream out of a squirt gun.

The pump can be replaced without removing the carb, you just carefully remove the carb top cover (watch out for the small parts!) Do it carefully without damaging the gasket and you will not have to replace the gasket. I do not think there is anyway to fix a worn out pump piston, they come in a carb rebuild kit and it might be possible to just purchase the accelerator pump by itself. While you have the top off you can also clean out the gunk in the bowl and make sure the float and needle valve is in working condition. be careful you do not blow out the small check valves, some have tiny springs behind them and some do not. They are tiny steel balls that go into the passageways and act as one way check valves.

I do not think it is a bad choke, that would only affect cold starts. Once the engine is warmed up it would run normally. Unless it was stuck part way open, not fully closing and not fully opening. You might check it for normal operation. take the air cleaner off with the engine cold, and see if the choke closes when you hit the throttle, start the engine and than watch for it to slowly open as it warms up (note: you have to cap off the vac line that goes to the valve on the bottom of the air filter housing).

You might consider doing a carb rebuild and doing a full system check per the FSM procedure, it will take care of all of these issues. If any one of these issues is bad it might be possible all the other systems will need service soon anyway.

But based on your symptoms I would say it sounds like a bad accelerator pump.

Good luck.

[reeder123]

Many thanks to both of you! I feel like I'm pointed in the right direction, I'll start with a thorough vac line check and then check out the accelerator pump and choke.

[EliRush]

Hi all, I am new to this forum, and to Toyota 4WD's. I was reading this one, read Petros' and other posts, ran out to cap off the vac line, and voila! Runs like a top now! Thanks!

[Scout23]

This is exactly what my Tercel is doing. I just posted a thread about it and then came across this thread. I have checked for vacuum leaks and replaced the AAP. Tommorrow I might replace the primary pump and see if that works. Hopefully one of us can solve the problem. Good luck!