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Matt
Matt, Engineer
Category: VW
Satisfied Customers: 16621
Experience:  Mechanical Engineer with 20 years experience in the auto industry, 8 yrs in formula 1 engine testing
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Volkswagen Golf GL: I have a 1994 vw golf 2.0 obd1 engine.

Customer Question

I have a 1994 vw golf 2.0 obd1 engine. I have a very annoying issue with it. The car almost every day will start hesitating only on partial throttle...for example when i am cruising at any constant speed and i let off the gas....then press the throttle again....it has no reaction for a few seconds...then it will all of a sudden react to the throttle. I have found that if it starts hesitating i can shut the car off and turn it back on while driving and it will drive normal for a few minutes but eventually start acting up again. Now i have replaced the tps, the throttle body, the maf, the ignition switch, relay 109 because it was burn out...due to a loose solder, already triple checked timing...it is dead on. replaced spark plugs...spark plug wires are new, new coil, ignition module, head gasket, intake manifold gasket, exhaust mani gaskets, fuel filter, speedo sensor, oil pressure sensors, o2 sensor. The car has no secondary air, or ac, or power steering, or iac, due to the fact that i didnt want them so i took them out...before you ask...the car had the same symptoms before removing these as well. I have listened and checked for vacuum leaks but have not found any. all cylinders have good compression around 200 in all except #1 which is 198. Car does not hesitate when fully accelerating, only durring cruising or letting off throttle and re pressing.
Submitted: 2 years ago.
Category: VW
Expert:  Matt replied 2 years ago.
Hello

I have to say this really does sound like a vacuum /air leak and I'd try this method to double check for one.

The best way to locate a leak is to have the engine running and warm and then spray lighter gas /propane around each joint in turn. If the engine rev's up you've found your leak.

Work your way through each possible joint one at a time and you should find it. I use a slightly flattened piece of brake pipe and some rubber hose from the can of lighter gas to provide a spraying 'wand' and allow a direct blast of gas into each area, especially those difficult to reach with large implements.

It’s also worth getting the fuel pressure checked measured with a gauge as if this is low due to a faulty regulator or even a poorly pump will all result in insufficient fuel being delivered to the engine

I'd check the condition of the injector plugs / connections as this could be a lean misfire if an injector isn't firing properly - the best way to check this is with a 'noid' light

http://www.noidlight.com/

Then check all the connections to the engine sensors one at a time, remove each one and examine for signs of corrosion or damage and a squirt of contact cleaner ( not WD40) will also help.

Customer: replied 2 years ago.
Relist: Other.
answer was already done and stated in the question
Expert:  Matt replied 2 years ago.
Hello

OK

if you're certain that there's no air leaks, the sensor connections are all Ok and the injectors are all firing correctly

You make no mention of measuring fuel pressure and this could be an issue as its should be 3.0 Bar - if a little low this can produce the hesitation you describe

also I'd consider replacing the water / coolant temperature sensor as this has strong effect on the fuelling and its not expensive to replace
Customer: replied 2 years ago.
Ok so how does the coolant temp sensor affect the fueling? just curious...
Expert:  Matt replied 2 years ago.
Hello

a cold engine needs a rich fuel mix as the cylinder head and inlet manifold surfaces aren't hot enough to provide any evaporation so you need extra fuel to give a mixture that will light off in a cold combustion chamber

and a good way of measuring engine temperature is to use coolant temperature so this sensor has a strong effect on the fuel mix as the ECU can add another 30-40% of fuel until it thinks the engine is up to temperature

therefore if the sensor is faulty then it can fool the ECU into providing extra unwanted fuel
Customer: replied 2 years ago.
yea but how does that affect the motor after it is already warm? Is there any way for me to diagnose the sensor? or even test wiring to see if there is a problem elsewhere?
Expert:  Matt replied 2 years ago.
Hello

you're right when the engine is warm the coolant temp sensor shouldn't have any effect


however if the sensor is faulty then this is where it can cause issues as it'll tell the ECU the engine is cold, when it isn't resulting in a load of extra fuel being dumped in

you can measure the resistance of the sensor at the extremes of temperature ( use water ice and bolling water) when its hot the resistance should be in the region of 200 ohm and and 9-8Kohm when at freezing

however the parts is about $20 to replace so it may be better to just replace it
Customer: replied 2 years ago.
I just replaced the sensor and this did not fix the problem....is there another thing i can try? any way to test ecu issues? or would that not cause this? It just feels like something is sticking...or not reacting when i press the gas...its just kinda bogs...the motor sounds like its getting the gas but there is no acceleration for a second or two....any way to test the maf to see if its defective?
Expert:  Matt replied 2 years ago.
Hello

thanks for the extra information this does reinforce that it could be the MAF meter

Might also be worth checking the wiring and connector to the airflow meter for any signs of corrosion or damage. you can do a quick fault find if you unplug the meter and run the engine without it.

if the engine condition is the same as when the meter is connected then chances are the meter or the connection to it is faulty

But there's no measurement across pins that can diagnose the meter I'm afraid

Customer: replied 2 years ago.
What about the tps....I thought that was the problem to begin with but i replaced it and there was no difference. I also tried unplugging that and driving and had the exact same symptoms but much worse...I replaced it with one from a junkyard...but have done that 3 different times...also the wires into the connecter have been crimped together because there was some cracked wires at the plug so i stripped them and crimped them back together
Expert:  Matt replied 2 years ago.
Hello


the TPS shouldn't have a big effect as its used to switch the engine into idle mode and also help with providing acceleration / transient fuelling


But this does seem to fit your issue - however if you've replaced it then the sensor should be fine so its worth checking over the wires all the way back to the ECU

to save time I'd suggest getting the car plugged into a diagnositc tool that can see the signals coming into the ECU - this will get to the issue quickly and save you money

If you find a VW specilaist these are a lot cheaper than using the main dealer but have the same level of kit usually
Matt, Engineer
Category: VW
Satisfied Customers: 16621
Experience: Mechanical Engineer with 20 years experience in the auto industry, 8 yrs in formula 1 engine testing
Matt and 10 other VW Specialists are ready to help you
Customer: replied 2 years ago.
What if the problem is not present on idle?...The only time i feel the hesitation is on partial throttle...The thing that keeps getting me is that it hesitates in the same spot every time. (partial throttle). even if i am at higher rpms it does the same thing....as soon as i try to keep the pedal in the same position or slightly let off...it will start the bucking....and will hesitate upon repressing the pedal. Now what are the sensors/parts of the car that are being used at this time? From the pedal it is the throttle cable, to the throttle body, butterfly valve, tps, maf, spark....combustion...and the ecu fits in there as well...
Customer: replied 2 years ago.
Also just rewired half of the harness to the tps...all three wires have been replaced, soldered in place and heat shrunk.
Expert:  Matt replied 2 years ago.
Hello

you've got the sensing path correct so its :

pedal opens the throttle via cable - so its worth checking that this runs freely and that there's no slack in the cable
the throttle opens so drawing in more air through the MAF and at the same time the TPS sends the rate of pedal acceleration to the ECU to add extra transient fuelling
the ECU will also read in the signals from the air temperature and coolant temperature sensors and offset the amount of fuel appropiatly

as the TPS signal should now be robust and you've replaced the MAF

have you tried unplugging the MAF and seeing how the car drives without it?
Customer: replied 2 years ago.
yea i did...the car drove normal i guess you would say....it didnt have as much power...but i only drove it about a half mile down the road.
Expert:  Matt replied 2 years ago.
Hello

So you didn't have the hesitation / flat spot when you drove it with the MAF unplugged?
Customer: replied 2 years ago.
no i didnt. Idk if it was just cus i didnt drive it far or what but it was less than a mile down the road so...
Expert:  Matt replied 2 years ago.
Hello

I'd have thought that would have been enough to show it up

Have you replaced the MAF

reading back through I'm not sure?
Customer: replied 2 years ago.
yes i did replace the maf....not with a brand new one. but cleaned with maf cleaner before installing...and also tried putting my old one back in to see if it changed but it didnt
Expert:  Matt replied 2 years ago.
Hello

you can also check the resistances on the MAF as its a swinging flap type?

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Customer: replied 2 years ago.
i dont have a flap type maf....its just got a part sticking inside of the tube with a flat computer board looking part on it.
Expert:  Matt replied 2 years ago.
Hello

in that case thats a hot wire type so disregard the resistance information
Customer: replied 2 years ago.
ok....so is there any way for me to test the one that i have?...i would just buy a new one but they are not very cheap so if i can diag before buying then that would be great
Expert:  Matt replied 2 years ago.
Hello

With the MAF plugged into the car and the engine running if you probe the back of its plug for voltage across pins 1 & 2 then at idle you should have 1.2 V and at 3000rpm 1.7 V

I think the only thing that's not been covered here is having the ECU tested for correct function

it may be worth sending it off for inspection by a firm like this


http://www.ecmtogo.com/
Customer: replied 2 years ago.
Well i just tested the maf...and i wasnt sure which wires were 1 and 2...but i tested the two on the left and two on the right...the two red wires had 14.22 v while idling...and the two on the left...two orange wires didnt have any voltage...i tried switching pos and neg and still got nothing...
Expert:  Matt replied 2 years ago.
Hello

there should be 3 pins is this correct?
Customer: replied 2 years ago.
no....its a 4 pin connector
Expert:  Matt replied 2 years ago.
Hello

if its 4 pins then it should have the following signal

Pin 1 = ref 12 V
Pin2 = signal out
Pin 3 = ground
Pin4 = signal ground


with pin 1 being closest to the rounded end of the connector

so test for voltage between pins 2 and 4 for an output voltage that varys between 0.5- 4.5V

at idle you should have 1.5-1.7v and if you very briefly give it full throttle a 'blip' you should get 4V briefly
Customer: replied 2 years ago.
i tested this today and i got around 1.5 volts at idle....but when i gave it full throttle...it only got 2.33 volts. I also tried slowly increasing the throttle and the voltage went up and then stopped at around 2 and wasnt constant. I took my maf of today to work on my intake tube...and now my car wont idle at all...and my cel came on with a maf code....i ordered a maf from a parts store and they said i could try it out first and see if its the problem...i will be doing that tomorrow
Expert:  Matt replied 2 years ago.
Good luck

hopefully this will resolve it

don't forget to carefully check over the wiring and connection to the MAF as well
Customer: replied 2 years ago.
so the brand new maf did not fix the problem at all. I dont know what else to check...
Expert:  Matt replied 2 years ago.
Hello


I agree its getting difficult to think of other possibilities I'd say its at the point where the car should be plugged into a dealer level diagnostic device - the type where sensor inputs into the ECU can be read off a laptop or similar - that way you can see if all the readings into the ECU are within parameters

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