I have been having consistant idling and surging problems with my brv for the last couple of months. When I first start her up in the AM she surges...sometimes violently, sometimes not. Within the last week, I have checked all the vaccumm hoses for loosness and cracking. It stopped briefly and then started again. I have adjusted the idle, which someone suggested I try, because right after the surging would stop it it was idling at 1100 RPM! So i tried it, now the idle seems quite low and within the last week when idling it makes a guh-guh sound and sounds as though it is going to stall, sometimes it does sometimes it does not. I am new at self diagnosising my car. Anything with the drivetrain and supension I can handle (The last volvo lost its rack and pinion in a huge NYC pothole), but fuel, air problems...not so much. I thought about taking it in for a diagnostic check, but thought I would try to figure it out on my own. These are my thoughts;

I need to change the idle control unit

I have some sort of fuel delivery issue (But then again the car seems to do the same whether full or close to empty, and I have already tried the fuel cleaner stuff my mechanic suggested)

I have some sort of amp issue with the ignition or the main fuel pump relay.

If I am headed in the wrong direction...please stop me.

What Josh said...plus, continue to check for vacuum leaks, the source of an idle surge on my '81 242t. Spray carb cleaner or WD-40 at all the vacuum hose junctions with the car running, if the idle speeds up, you've found your leak. I tried this around my injectors and found that 2 of the 4 had leaking seals. I replaced the seals and the car idled normally again.
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don hodgdon '89 744ti, '81 242t, '71 D-35

Bitching about perhaps having a grimey idle air control (IAC), it's located under the intake manifold. You'll have to take it out and clean it with carb cleaner, the two large hoses that go in and out of the intake manifold lead to the IAC it regulates air and is a little motor that opens and closes a little door, and a little mouse lives in it with a little piece of chee....wait a second.

Yank the IAC out of the car and run carb cleaner through it, fill it, cover the holes with your fingers, shake it and repeat the process until the carb cleaner runs clear. After that and in addition to, clean the throttle body (TB), the TB contains the butterfly that actuates when you hit the gas, that thing is grimey and must be removed from the intake mani., get a new gasket and a small brass brush, spray it with carb cleaner and scrub the crap off the inside of it. This cleaning may also necessitate a real adjustment of the idle.

Also clean the flame trap, it may be housed between the last two fuel injectors and prevents backfires, if it gets clogged you will be adding pressure to your engine seals, it is hidden, so be brave and grab it, it's about an inch in diameter and is inside the larger hose and at a bend pull it out and clean it with carb cleaner, need more info on that, do a search. A small hose runs from the side of the flame trap unit to a small brass fitting on the intake mani. this fitting can get clogged too, stick a paper clip through it to make sure it's clear. Hopefully this will help. And as if I haven't rattled on enough you should also look into replacing your engine wiring harness, if you plan to keep the car. Volvo's wiring harnesses were clad in enviormentally friendly insulation that eventually fell off the wire, resulting sometimes in an erratic running condition. You do have the option of rebuilding the harness but you can buy one at www.ipdusa.com, install it yourself it's not brain surgery. Allright if you do that then you can keep the car and tune it properly and drive it for a long time which precludes buying a new car and paying a car note on something no doubt inferior to what you've got now.

Josh

A new wiring harness at IPD is $500. Is that the best way to go?