BrickBoard Archives
The files contained in this listing have been automatically archived from the active forums. Because the vast majority of posts are now in one place, this archive is considered legacy. You should use the SEARCH feature OR choose your topic and select date tabs within the forum you choose.
Erratic Idle - '89 744 B230F[ALL/1998] posted by Lee Lowrey on
Tuesday, 23 December 1997, at 7:33 p.m.
Wife's '89 744 (stock B230F with 125k miles) had a very rough idle a couple of weeks back. The car runs fine on the road at any speed, just a bad idle. I followed Haynes' idle adjustment procedures and degunked around throttle valve to no avail. Took out and doused air control valve with carb cleaner, which seemed to help. Relaced air control valve yesterday, but now I have a different idle problem. The idle speed now surges up and down in a 500-rpm range in a regular 2-second cycle. Over the holidays, I'll re-adjust the idle link rod and check all of the visible vacuum hoses and electrical connections. Has anyone experienced this problem and/or have any fixes that may be quick and easy? I can't get too heavily into expensive parts or a lot of personal labor (my '94 960 needs new tires and I need to put new front wheel bearings and tie rods on my eldest son's '89 M-B 190E next month). Intake manifold leak? Plugged flame trap? Bad oxygen sensor? Appreciate anyone's help...
Re: Erratic Idle - '89 744 B230F[ALL/1998] posted by Dave Stevens on
Wednesday, 24 December 1997, at 11:35 p.m.
Sounds to me like you've still got an idle air valve motor problem. Did you replace it with a new one or a used one? If you went for used and the problem changed, but didn't go away, then perhaps the replacement was also less than perfect.
When the idle is bad, tap on the idle air valve with a large screwdriver handle and see if the idle returns to normal. If so, then you've still got a sticky valve. Even if the air passageway and valve are clean, the valve can stick slightly resulting in erratic idle speed, especially jumps in idle speed. This can be caused by grooves worn into the commutator by the three contacts (the commutator spends its whole life twisting back and forth in a relatively small arc). As you've now probably got a spare one, why don't you try pulling one apart as follows:
-Mark the casing for reassembly, open up the crimped tabs and slide the casing straight up and off (note the flat and bevelled washer on the shaft).
-Clean the commutator with light abrasive (like fine emery cloth) to eliminate the grooves and polish as best you can.
-Put a drop of light oil (like 3-in-1) into the bearing sleeves.
-Carefully push the casing back on, twisting back and forth to allow the bevelled washer to open up the three contacts.
-Press the crimp tabs back down (a suitably sized slot screwdriver and hammer is all you need).
The valve should move quite freely when you're done. Good for another 50k if you're lucky.
Other ideas:
-Inspect main intake air hose between AMM and throttle body for cracks/leaks.
-Inspect air filter box thermostat flap to make sure it closes properly when engine is fully warm.
-You've got the throttle plate area nice and clean, good. As you said, you do need to check and clean all vacuum hoses and manifold fittings, especially the small hose from top of the flame trap.
-Make sure the throttle switches are working. If you know how to use your LED diagnostic socket there is a test for this, but an ohmmeter will do.
-The next thing to do is a full check of the throttle body adjustments as you indicated, but make sure you've got the proper procedure. As I recall, Haynes may be a little light in this area. (eg. don't just test for click-click on the throttle switch, make sure the gap is right with a feeler guage). Unless these settings have been tampered with or the throttle linkage rod lock nuts are no longer doing their job, you may be better off leaving this area until after you've fully attacked the above.
Re: Erratic Idle - '89 744 B230F[ALL/1998] posted by Lee Lowrey on
Saturday, 27 December 1997, at 1:22 p.m.
Thanks for the tips, Dave, but my problem's been solved. I did replace the air control valve with a new one. Calls to all our local parts suppliers resulted in the Volvo dealer having the least expensive ACV -- exact Bosch replacement was $142 with tax. I will take apart the old ACV and refurbish per your instruction (keep it as a spare, or give it to my brother-in-law, who has an "88 744).
Here's the chronology of my fix: 1) cleaned out the flame trap -- the vacuum nipple was plugged; 2) replaced both vacuum hoses to the intake (from flame trap and from the valve at end of fuel rail), since they were pretty hard/brittle; 3)adjusted idle linkage per Haynes (they do spell out the feeler guage procedure well); 4) reset the throttle switch; 5) upon hearing a faint air leak, tighted the intake manifold nuts, which were pretty loose; 6) still heard a faint air leak, so I took a feeler guage (0.040" used in 3 above) and started feeling around the gap between intake manifold and head -- immediately found the leak at the number one cylinder (apparently I had pushed against the gasket protruding at the gap when I was holding the intake while replacing the ACV); 7) bought a new intake manifold gasket at the local Volvo dealer (for $17 including tax, just fifteen minutes before they closed on Christmas Eve) and replace the brittle (original?) red gasket with a nice, rubber-like, grey-colored gasket; 8) wife's car now idles smooth as silk at 750 rpm (in park or in drive with the brake applied) for the first time since we bought it -- it used to idle best at 900 to 1100 rpm.
Definitely a lesson on periodic inspection of all exterior engine components pm our older cars...
Have a safe and enjoyable New Year!