Pontiac LeMans 1.5 engine vibration

hotpig175 · Post by **hotpig175** » Sun Oct 14, 2007 2:20 am

Hi... I have a '90 Pontiac LeMans 1.5 Automatic, (lucky old me...), which goes ok for what it is, but it vibrates like nothing on earth when it's at low revs.

I've actually owned this car twice, over a period of about 4 years, and it's always done it, but seems to be getting worse lately. I've had to crank the idle up to around 1500rpm in neutral, which solves the vibration issue, but I imagine this isn't good for it.

The engine mounts APPEAR to be in good shape - I don't notice any clunking or other strange noises when going in or out of gear.

I'm wondering if maybe the ignition timing is out, but cannot find out what the specification is for this engine - most of these beasts were sold here in NZ as the 2 litre version. This is a 1.5 litre SOHC carburettor engine. It's had a new cambelt, a new ignition module and plugs/leads etc, plus gets fairly regular services, and actually drives really well otherwise.

Any ideas?

Spider · Post by **Spider** » Sun Oct 14, 2007 2:54 am

Don't know if this will help you or not but for what its worth ?

I had a bad front motor mount on my Lanos.
It 'looked good' but the rubber part of it ( the part that you can't see when the mount is installed?) was cracked.

Welcome hotpig175 !

hotpig175 · Post by **hotpig175** » Sun Oct 14, 2007 6:59 am

Thanks for that, Spider.

When it stops raining, (If...), I'll whip ém out and have a look at them.

Are they the same as the 2 litre mounts, and are they the same on later models, e.g. Lanos, Cielo etc?

GsiTurbo · Post by **GsiTurbo** » Sun Oct 14, 2007 4:23 pm

So do you feel its the vibration caused by the bad mounts, or the engine timing? You said the motor runs fine otherwise - what mileage do you get (its always good indicator). Is it the carburetor, or perhaps throttle-body injection (single injector in a housing that looks similar to carburator)? If memory serves me well, on 1.6 TBI SOHC model, base timing is 8 degress.

hotpig175 · Post by **hotpig175** » Sun Oct 14, 2007 8:30 pm

Hey...

Thanks GSi Turbo.

It's a 1.5 carb motor. I'll try setting at around 8-10 degrees at say 750 rpm, and see if this makes any difference.

Mileage is generally pretty good, unless you flog it, which is a waste of time anyway...

Cheers for that.

GsiTurbo · Post by **GsiTurbo** » Sun Oct 14, 2007 9:41 pm

As a quick note, if your motor is equipped with the ALDL connector, it has to be grounded to bring the motor into the base timing mode. Otherwise, your electronic ignition will be adjusting in, hence providing incorrect reading. I remember during the time I had 1.6 Lemans (auto), It did develop nasty low rpm (below 2000) hickups, which turned out to be caused by bad distributor cap/rotor assembly. You may want to check those as well. Hope this helps.