I've been working on a 1991 Laredo with a (stock) '96 motor, and have been having a weird couple of issues that I suspect might be linked:

The engine starts and idles really nicely for 30 to 90 seconds, then starts to get rough. It'll choke down, then the computer will let in more air, and it will rev up to 2,000 rpm. It does not have the power to pull itself forward very far.

The Bendix 9 brake system is acting really weird, too. When the ignition is "ON", and I press the brake pedal, a weird vibrating, like belching, noise comes from aroundabouts the Charcoal Canister -- I've seen and felt the cap on the top vibrating.

Any advice on how to proceed is greatly appreciated!

Thank you!

Spencer c]:^)

 

Check the integrity of the hose from the intake manifold to the MAP sensor on the firewall first.

Verify your intake manifold bolts aren't loose and you have no vacuum leaks.

 

I checked the manifold bolts, and it turns out the torque wrench I was using was severely inaccurate. I re-torqued the manifold bolts, and the idle is much better. It still coughs a bit on start-up, but I suspect that's because the motor hasn't had any real load for more than a year.

Before I had the opportunity to start it, the battery was very low, so I checked for the weird brake pedal vibration "belching" noise, and heard distinct clicking (and saw distinct shaking) from the ABS Booster Pump and Motor unit. The brake pedal does not return under its own power, either. I still need to take it to DEQ; how should I go about tackling this problem, and what might the problem be?

Thank you!

Sincerely,

Spencer c]:^)

 

As far as the intake manifold bolts go, the factory torque spec was too low.

Better off using the human torque wrench method.