200•700•900 Series Product Specials for May-June 2009
Page 1: AIR INTAKE: Filters, Hoses, HD Vac Line Kit, Flame Trap Kits, Cold Air Intake Advice

TECH TIP: Air Intake System Basics
by Rob Arnold, Product Development Engineer
 
Often overlooked due to the fact that it when it leaks you can’t see it, the air intake system on your Volvo is a very important system that can effect performance just as much as a fuel or water leak. The basic components include the air filter and air box, associated plumbing and tubing, intake manifold and depending on the model an air mass meter, throttle body, carburetor, air flow meter, constant idle speed motor or auxiliary idle valve and air box thermostat.

If you are not familiar with some of these components, but would like to learn more about them a good shop manual will help explain the function of each part and what symptoms they exhibit when they fail.  Problems associated with the air intake system usually result in too much air (lean condition) or not enough air (rich condition) entering the engine. If the leak is severe enough, it will effect the idle and drive-ability. Lean conditions result in difficulty starting when cold, backfiring or engine knock upon acceleration, and increased operating temperatures. Rich conditions due to air restriction lead to sluggish performance, reduced fuel economy and possibly black smoke out the tailpipe.   

Lean Conditions
Look for leaks in the intake system, commonly referred to as vacuum leaks. Common problem areas on Volvos include cracked or broken vacuum lines attached to the manifold, visually check both ends of all hoses. Broken or split hoses are very common in 200 and 700 series cars and some are difficult to see as they connect under the manifold. Clean up the engine compartment and use a flashlight to get a good look. Replace damaged hoses as clipping the ends and re-installing will only last a short time, a very short time!

 Broken intake manifold gaskets or leaky injector seals can be checked using a spray bottle filled with water. With the engine running, spray water at any areas you suspect may be leaking. If the idle drops, you’ve found your leak as the water has momentarily sealed the leak causing the idle to go back to normal. Dried up and shrunken injector seals will have to be replaced, sometimes intake manifold gasket leaks can be repaired by tightening up the fasteners, but if they feel tight, you’re probably going to have to replace the gasket.
Another common failure on 200 and 700 series cars from 1982 to 1995 is in the large plastic flex tube that connects the intake manifold to the air mass meter. This tube is routed close to the inner fender and if it is allowed to touch the fender a hole will soon wear into the tube allowing unfiltered and un-metered air to enter the engine. 

Rich Conditions
Biggest problem here is usually as simple as a dirty air filter, but there are a few other contributors to check out. 200 and 700 series use an air box thermostat to draw hot air off of the exhaust manifold to help speed up the warm up process. If the thermostat fails in the cold position  (and they usually do) super heated air will be drawn into the air box after the car has warmed up. This results in a rich mixture and is also very hard on the air mass meter and will destroy the air mass meter if left un-repaired. Any obstruction or crushed areas in the intake plumbing can cause significant reduction in airflow under load.