Poor Acc' when cold/Engine Light

[Cozy]

Had a problem with my 97' Sportage (UK RHD) for a few months now which until recently was intermittent.

When setting off from cold the car often hesitates when accelerating, this improves and is very intermittent once the car has 'warmed up'. I've read the codes from reading the 'flashing' MIL light and got the following... the cars diagnostics connector is the 20 pin type in front of the battery under the bonnet.

2 Distributor no Signal.
8 Mass Air Flow Sensor.
15 Oxygen Sensor.

The problems seemed to start following a service around 5 months ago, I've replaced all the spark plugs and replaced the MAS which I managed to lay my hands on but this hasn't resolved the problem.

To add to the mystery! - when coasting along on the motorway at 60-70mph the engine light has flashed up a couple of times only to go back off when I tap/press the accelerator a little more.

On a couple of occasions the car has also idled really roughly (i.e trying to stall when pulling up at traffic lights etc) but then after stopping the engine and then starting the car back up 5-10 minutes later everythings fine.

Anyone got any idea/clues?

[Cozy]

I've also disconnected the battery today and cleared the codes before taking the car out for a run.

Following on from this the 2 Distributor no Signal & 15 Oxygen Sensor codes have re-appeared.

[Harry Morgan]

What was done to the car when the service was performed 5 months ago ?

I'd tend to think that something in the service area might have been either damaged or not re-connected, etc.

Harry

[Cozy]

Hi Harry

The usual Air and Oil Filter, plugs. I've been over all the Rubber Pipes and everything looks fine/sealed up. Wondering if the Oxygen sensor has a bad connection and going to swap this out in the next couple of days if I can get my hands on one.

Anyone know how many wires the sensor has? The Motor Factors I phone earlier didn't seem so sure.

Cozy

[Steveo32]

It sounds like you may have a bad O2 sensor, and that would mess up the air mixture and give you at least two of the codes you have and would also account for the hesitation. Is your mileage different than usually ie less or more mpg? Could also be a crack in the gas tank that is causing water to get into gas tank and is freezing and allowing to much air into the fuel mixture. I would check your 02 sensors first, they are the easiest, if you have over 75,000 miles I would bet it is the o2 sensor or sensors, there are usually 3 one on manifold, one before catalytic converter and one after catalytic converter. The gas tank would have to be pressured tested by dealership.

[Cozy]

I've managed to get my hands on a Universal Lambda Sensor today so will look to fit that in the next couple of days to see if it clears the problem up.

Replaced the plugs as a matter of course just in case and noticed that the ignition coil body has split underneath the rubber HT boot/plug. Not sure if this could be causing a problem but think it's probably wise to swap these out as soon as I can whether or not the O2 sensor is or isn't the cause of the hesitation.

The MPG does seemed to have dropped but not too noticeabily, but I've tended to put this down to the cost of the petrol here in the UK and not getting quite as much for your money!

[Harry Morgan]

Cozy

If the O2 sensor fails, then the PCM will normally default to a "rich" (cold engine) mixture and, depending upon how much you drive, you may notice a decrease in mpg -- i.e., if you typically just go a couple of miles per trip, then you should not notice a difference, since its function does not kick in until you get to operating temperature.

Also, forget the downstream sensor (the one rear of the converter) as it exists only to signal the failure of the converter and has zip to do with the performance of the engine.

If you happen to have access to a scanner, you can graph the voltage to the sensor -- it should float/oscillate between approximately 0.1 and 0.9 volts after the engine has reached operating temperature.

Harry

[Cozy]

Just a quick update on my problem! I replaced the Oxygen Sensor and since then (2-3 weeks) the car has been running fine.

Harry, not sure how/why the oxygen sensor was causing the problem when cold if your above post is as/how it should work unless the sensor was acting as if the engine was upto operaing temperature?

I have read that some of the engine cleaning products used to 'clear' the engine when serviced can damage the sensor, I'm sure the mechanic said he'd run the engine through with something in it to clean it up when he serviced it so perhaps this could've been the root cause.