'99 1.8 16v engine hesitating (again)

[pphilpot]

OK, so status update 2.

Car is still hesitating badly between 2200 and 3500 RPM.

Changed the coil pack, the stepper motor and the lambda probe.

The hesitation is occurring when hot and cold. I've just taken off the throttle position sensor and measured the resistance, and it appears OK in steps from 0.9 to 2.8. Can I rule this out? My thinking here is that it's done 177000 miles and the hesitation is at about cruising speed in 3rd, 4th or 5th i.e. the average settling pressure for the throttle pedal, and maybe the potentiometer inside the TPS has bad contact now in that region - although the multimeter suggests not.

When I disconnected the lambda probe, it drove well. Now with a new one the problems are back - including slightly erratic idling when cold (hunting really) and then it settles down after 30 seconds to a minute). When I disconnected it, did the ECU just ignore all sensors, and therefore hide the problem elsewhere? With it running well while the lambda probe was disconnected I can also rule out a fuel problem I assume.

As it's happening when cold and hot, can I rule out the coolant temperature sensor? I suspect that the thermostat has gone though as it sits at about 75° when cruising, and at 90° in traffic - but I can't see that influencing the problem.

Is the MAP sensor easy to get to (i.e. where is it )? - I'm thinking that all that's left

Thanks in advance for any help.

Cheers

[abonet]

Hi, same problem here. I've changed lambda sensor but it still hesitates. When disconnected, the car drove well, but once replaced, it started with the problem again. The map sensor is here:


It's under the admission collector.

It's the number 5, sorry for the language in the description field, but i'm spanish.

Did you finally replaced it? Did it make a difference?

Many thanks.

[pphilpot]

Hi abonet

I solved mine by tracing back along the wiring loom of the sensors and found that a design fault had led to some sensor wires rubbing on the engine block and causing them to short.

This is what I wrote here: viewtopic.php?f=3&t=11976#p105815

OK, so every time I post on here it encourages me to get back out there and get under the bonnet.

The problem is that wires have chafed causing a short - this appears to also be causing the hesitation.

It must be a design fault, so this may prove useful to others who have the hesitation problem. If you follow the loom from the ECU down behind the inlet manifold you'll get to where the wires for the throttle housing sensors come out of the main loom cluster. This is poorly positioned and mine was resting on a sharp metal support running horizontal to the loom. Years of movement had rubbed through the grey and white wires running to the throttle body sensors. I'll solder these tomorrow, and I'm certain that my fuse blowing, rough idling and annoying hesitation will be a thing of the past.

Initially me car was just hesitating, but the fuse blowing started on occasion, but soldering this wire cured it.

Hope this helps your problem...

Cheers

Paul

[abonet]

Ok, I'll take a look on mine. What I don't understand is: why the fault manifests only at those rpm? Because of vibration?
What was the fuse blowed? (I mean what part of the car was protected by that fuse.)

[pphilpot]

Hi, it was fuse 27 that was being blown (on occasion, and got worse) which protects a number of components including the ECU.

Here's how my problem was:

When I disconnected the Lambda probe it essentially stopped the ECU from looking for sensor data and therefore stopped sending current down the broken sensor wire - that resulted in no hesitation because there was no shorting. Whenever I remove/replaced another sensor the problem initially went away, but then returned - this was because the broken wire was being moved away from the engine block slightly stopping it from shorting. Of course as the miles went by the wires would settle back to their position and short again.

I can't remember now which sensor the broken wire went to, but it was on the throttle body (there's a few there), so likely influence why it stuttered in a certain rev range - i.e. that sensor was being called on in that rev range and the broken wire would then short. But it also could have simply been vibration.

Hope this helps.

Cheers

Paul

[abonet]

This helps a lot, many thanks!

[abonet]

Hi, I´m still having this stupid hesitation, and it comes to worst on gear change, from 1st to 2nd it´s horrible if I don-t rev up above 4000.

Could you just post a photo or a paint jpg with the exact location of your rubbed loom? Many thanks

[pphilpot]

Hi, here you go. Basically it's under the inlet manifold, just to the right. You'll note that I popped a 10mm sleeve of pvc pipe over the sharp(ish) section of engine that caused the wires to rub and short out.






Good luck with it - I know how annoying that problem is!

Cheers

Paul

[abonet]

Thanks! I´ll give it a look! And yes, it´s really really annoying

[omega]

i can solve your proplems for 70 pounds





buy my sweet running 2.0 liter engine