I have just purchased a 1998 malabu with a 3.1 engine. It has a rattle when cold. Any ideas? I've been told not to worry.

Yes they are prone to piston rattle and rocker arm noise until the lifters pump up. These types of noises are nothing to worry about unless they don't go away after a few minutes of run time.

Does the check engine light go OUT while cranking? If not , if it stays ON, you've got a bad crankshaft position sensor. These can fail with intermittent no starts. So just when you have it towed it, it'll start working again. Check engine light is supposed to go OUT if it's getting good signal from the sensor.

you need to put gauges on it and see what the pressures are to see if the compressor is working while your waiting for that is the compressor running? is the large ac pipe cold?is the smaller pipe hot?

Didn't say if you pulled the sparkplugs on 2 and 3. Are the plugs good and not oil fouled? Also, possible they got a crack in their porcelain when putting the engine in. Do a compression test and see if all cylinders have good compression, especially 2 and 3. Check the distributor cap and rotor for wear. Just throwing out a few suggestions, Jack. (Sure wish I had your webers.) Good luck. Do let us know the outcome.

Sounds like an exhaust shield rattle, the brackets that secure the heat shield in place come apart due to rust.

this case .you have to check compresion of all piston first then compair it before you go out to ignition coil . exhaust and intake valve have lose compresion may be in piston 3 . check spark plug No.3 have oil or not complete burn . make sure compresion is ok then check igniton coil .and injector if same modle . but i don't think exhaust have eny problem and if there is it will be for all misfiring not only No.3 check some time comes when lose vacum .

you need to turn on the a/c and watch the electric clutch engage on the front of the compressor. Sometimes, when the clutch gets hot, it won't lock up and lock the compressor to the pulley. You might be able to adjust the gap closer, or replace the clutch. Might have to pull the comressor to do this. If you had a leak, it never would have strated working.

This "rattle" is most likely caused by fuel knock and is not injurious to the engine. However if you wish to rid yourself of listening to the sound, you'll have to purchase a higher grade(octane) of fuel. Thank you, Dana

could be coming from 3 spots
1 engine mounts = mounts go bad try shaking the motor when its cold to see if you can hear it
2 brakes = sometimes brake hardware can come loose or rust away mo so in brake drums in the back
3 exhaust shield = there is a thin shield around parts of the exhaust while it cold shake the tail pipe to see if you hear it

you have answered your own question ,also a regrind of crank wouldnt go far amiss