It has a 1.8 L motor, automatic transmission. When I try to accelerate from a stop, regardless of how much I depress the gas pedal, the car will take 1 to 3 seconds to really accelerate over a very low minimum. This problem is now intermittent. I have changed the spark plugs, coils, crankshaft sensor, camshaft chain system, cleaned the camshaft sensors and MAP sensor. There are no error codes. On 2 occasions when it was running with no acceleration problem and hit a pot hole it started to have this acceleration problem again. It might also sputter on acceleration from zero. At times the motor will shut off on zero gas pedal position. I'm thinking there might be a bad electrical connection somewhere, but where do I start looking?

 

When the vehicle is idling , feel the exhaust. Then have someone raise the engine speed to over 15oo RPM and feel the exhaust . You should feel a big difference in pressure coming out of the exhaust. If not, exhaust converter could be restricted.

 

If this was the problem, the car would have an acceleration problem more at high speed than under 1200 rpm? The problem is in the first 3 seconds of acceleration from a stop. Otherwise there is no problem and it doesn't always happen.

 

You can look all you want, but we need to see just what is or is not happening and a scan tool will be required to see just what the parameters are when the problem takes place.

I suspect there is a problem with the throttle body, which is expensive and before spending a lot of $$ verify what we suspect.

 

A good friend of mine is very well known as a mechanic and specially as a scanner. He has an oscilloscope, with 8 channels so we can check everything at once. I did som experimenting and when I was stopped at a traffic light I would use the hand brake and not the foot brake. Doing this did not produce the problem. If it has something to do with the vacuum, I don't know why I don't and engine code or any other code.

 

Vacuum leaks do not generally produce a code unless the mixture is affected and then the oxygen sensor compensates for that , but if bad enough will produce a lean mixture problem code.

What I would do is , connect all 8 channels of his scope to observe the parameters of system voltage , voltage available at the ignition system, injector operation, throttle position, air flow, fuel trims, O2 readings , cam sensor and don't forget the evap system valves all while the vehicle is being driven.

That info can be captured on the scope and reviewed ,where if momentary the PCM will not capture that.
Would like to know what you find, thanks.

 

Thanks,for your reply. I definitely will get back to you on what we find.
I just drove several miles with stop signs and traffic lights with zero problem, then at the next stop I had the problem. Yesterday it even coughed or backfired in inicial acceleration. This is maybe the 4th time it has done that in 2 months.

 

You have the perfect tool to capture the cause of this intermittent problem. The only hard part is,,,,,,,,,,,,,,the scope must be connected every time you drive the vehicle.

Don't know if your friend can allow for this.
If that scope is connected and working anytime you drive the vehicle , when it does happen , you will have the conditions to examine at the time and pin down the cause.
You guys can do this ! Would hope you will share either the cause found or post the parameters at the time and sometimes 2 heads are better than one, lol, thanks.

 

Hi Hank, I still haven't been able to put the scope on my car, my friend just hasn't had the time. There was a code for rich mixture and the car is consuming much more gasoline in city driving, but almost normal on highway driving. My friend is still with the idea that it is a bad plug or coil. The canner showed this also, "OBD requirements for which the vehicle or engine is certified. OBD 1" .

 

You might want to ask, if it is a bad plug or coil why doesn't it throw a code for that ? The vehicle most times will record a misfire and that should show up with a code and might even tell which cyl.

A rich mixture is not always the result of a misfire. If incorrect info of air entering the engine is being sent to the computer, it makes adjustments for that and in this case it could be adding fuel when not necessary..

Is it possible to post the engine data stream info for us to look at?