hesitant corolla

[kazual]

My son drives a 1993 Toyota Corolla. It has a 1.6 L engine and automatic. It hesitates when starting out in 1st gear when the engine is warmed up. He also says it runs smooth when it is cool. Tune up was done, air filter good, fuel filter good and we ran a few doses of fuel injector cleaner. He tries to use Shell gasoline for its cleaning abilities and it seems to run better. We even changed the oxygen sensor. No check engine lights. What am I missing?

There is only 115,000 miles on the car.

Thanks ahead of time.

 

[Quest]

If it runs ok when cold and yet hesitates when warm, check the EGR valve and vacuum hoses/switches for leaks.

If your engine still comes with those vacuum/mechnical centrifugal advance type distributor, check the entire distributor advance mechanism for general leaks and sticky mechanism.

Also check fuel rail pressure, spark plugs (always buy/use NGK!!!), check spark plug cables for wear and HT leaks; OE distributor cap and rotor, etc.

Have you replace the timing belt yet?

Any CEL code?

 

[CBDFrontier06]

Don't know if this will help you or not, but my 94 Eclipse developed a hesitation when warm and it was a bear to track down because it ran flawlessly when cold. Finally traced it down to a bad spark plug wire. That was the first time I'd ever seen a spark plug wire behave differently depending on temperature....it'd been my experience up til then that when it's bad, it's bad. Not the case.

 

[trixman]

I had a 90 and a 91 rolla...same engine. With a lot of city driving it had a tendency to build up carbon in the combustion chamber and exhaust. If you needed to pass emissions soon, it would probably fail NOX.

Injector cleaner is good but won't clean a lot of build up.
You may want to introduce a cleaner ie B12, seafoam, H20 directly into combustion chamber thru a vacuum line while you fast idle (1500 to 2000 RPM) the car.

 

[Quest]

unless you meet/fulfill the following conditions, otherwise, I would not make the assumptions of having excessive amount of carbon in combustion chamber:

-lots of short trips ( -thermostat not closing/engine runs cold
-skipped some scheduled tuneups
-running some cheap gas

While it is not a bad idea to run something in the combustion chamber to clean things out a bit in general, IMHO most small engine imports engine runs hard and hot, and also given the fact that it's EFI variety (more precise F/A control), I would not take it like I would normally deal/handle with the old carb'ed varieties.

I always focus on the fundamentals first, before I move on to the less-obvious things.

My 2c's worth.

 

[kazual]

We changed almost every part you guys had mentioned. I am going to check the spark plugs and wires to see if one is at fault.

Thanks

 

[Quest]

check for vacuum leaks:

intake manifold gasket leaks, cracked vacuum hoses, etc. On a rare location, vacuum leak may appear in some of the least expected area (such as brake vacuum booster diaphram, etc.)

 

[alanu]

When the engine is cold its in open loop so the car runs rich. As the temperature goes to operating temps the a/f ratio goes into "normal" operating perameters.

Sometimes even a coolant temp sender will confuse the engine.

AT operating temps: If theres an intake leak try spraying some carb cleaner around the mating surfaces of the intake manifold (NOTE: Dont get spray happy) if the idle goes up you've found a vacuum leak (carb cleaner will enrichen the fuel mixture due to a lean condition from sucking air via vacuum leak)

If your gonna buy spark plug wires spend decent coin and buy NGK wiresets. Fits like factory. The newest premium line of bosch might fit well too.

 

[trixman]

Quote:

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Sometimes even a coolant temp sender will confuse the engine.

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I just remembered. On the 91 rolla, the connector to the above item was shorting. Evidently it frayed from taking the air cleaner assembly of a bunch of times with my fat clumsy arms for different maintenance procedures.

Check it out with a multimeter.Carefully inspect connector and disconnect.Test for 12 volts with ignition turn to on position (but not running of course) red to hot black to a ground.

If bad, may need to splice in a new one from the bone yard.

 

[mechtech2]

Good cold and not warm/hot means it's too lean - not enough fuel.
Does the car have a carburetor?

 

[PandaBear]

93 is fuel injected. I used to have the same problem and I later found that the spark plug is loose (____ Autolite quality control), and even tighten it up will still loosen it later. Replaced it with champion platnium and fixed it instantly. Cap and rotor makes a big difference too.