Engine Missing And Juddering In Low Revs

[steviewunda]

:o hi

my 2.0 petrol engine is missing and juddering in low revs.perfect on tickover and over 3000rpm.any ideas.apparently the rav 4 and picnic engine is the same.i have always fixed my own cars but these modern engines are way too complicated.please help as i am lost without points and distributer.

thnx in advance.

[rpaterson]

Without knowing the engine, all I can suggest is;

Check the coils

Check for vacuum leaks

Get the plugs out and see if you can spot what cylinder(s) are giving trouble

Is the engine light lit? Does it do it when the engine's hot OR cold or hot AND cold? My old trick is to disconnect Battery and unplug/plug back in all the connections you can find in the engine bay while checking for corroded pins or bad earths. Once you've done that, reconnect the Battery and see if that's helped. It might be a bit rough until it re-learns the basic parameters but 10-15 minutes should sort that out.

Loads of things it 'could' be;

Lambda

Plugs

Injectors

Coils

Temp sensor

Hopefully the above checks might find something.

[bothwell_buyer]

does your picnic have a 3SFE engine?? Ie up to about 2000 year age.

Ditto to the list from rpaterson. I'd look at the leads as well.

I'm trying to remember what it is on this engine affecting the low speed....see old age!!!

[rpaterson]

Not sure what the max resistance of the leads is supposed to be, but see if one or two are significantly different from the others.

[anchorman]

Start at the very beginning (thats a jolly good place to start)

From rp's list, put some plugs in as it sounds like something is breaking down under load. Be absolutely sure to fit the proper Iridium plugs as any others will give you problems.

[bothwell_buyer]

I'd also make the effort and feed it some higher octane petrol like wot comes out as Shell Vplus or similar. Don't tell me you've been feeding the poor thing supermarket sweep stuff.

[ahab]

Did you ever find out why your RAV4 was 'missing' as I have a similar problem?

Thanks,

[gjnorthall]

Your 97 model is significantly different to the 4.2 models discussed above. If the engine stumbles under load but it's OK at idle or cruising - it's often due to breakdown of HT ignition components - your engine has HT leads, distributor cap etc which can break down under load. Check if things improve after cleaning everything with a cloth moistened with WD40. Spark plug replacement may also be a good idea unless this has been done in the not too distant past.

[ahab]

Thanks for your speedy reply.

I did change all the spark plugs & it made no difference.

My first thought before I opened the bonnet was to change the main HT lead that goes to the distributor but the discovered that it doesn't have a distributor.

I was going to test all 4 HT leads next.

It mainly misses at lower revs - less than 2,000rpm but is better at high revs. I'll try WD40 but I have noticed that the problem is just as bad in warm weather as in damp weather.

I've never looked at a lamda sensor on any car so will have to resort to the manual for that (unfortunately I seem to have mislaid my RAV4 Haynes Manual, so have reserved one from my local library). I am hoping that it will tell me what resistance it should be at different temperatures.

Cheers, Ahab.

[gjnorthall]

Lambdas generate a voltage - not a resistance depending on the oxygen level in the exhaust gas - or more accurately the difference between atmospheric and exhaust oxygen. You can read the voltage with a digital meter - it should oscillate between a max and min level - a healthy Lambda should oscillate around 8 times in 10 seconds. Because of the feedback loop - measurements must be taken with the Lambda still connected or you'll get a strange result. The Lambda on your car will have a heater coil, the resistance of which will change with temperature.

The distributor in your case is a pair of HT coils - this engine doesn't have a conventional distributor.

You can't really test HT leads - a static test proves very little - the insulation usually breaks down under load. However with a bad set of leads - you can often see sparks jumping to earth if you observe the engine running in the dark.

[ahab]

Thanks for the info. I will get my DMM on the O2 sensor.

I was going to try to use a 'Megger' to test the HT leads, but it might not go to as high a voltage as the ignition system produces so still not a thorough test. I will try the test you suggested in the dark as well.

Cheers, Ahab.