Just bought my first volvo, an 87 720 GLE 4 door, manual transmission. Have a question about the idle...whenever i take my foot off the gas the rpm needle drops way down to almost 0. The engine has even cut off a few times because of this drop, even on the freeway when shifting. In lower gears, when shifting up or down the stalling doesn't occur. However, when i go to brake and leave the gas pedal alone, the needle always always dips down. Then the rpm's will steady out around 1000 rpm's. The needle was shaky even when idling the engine but i used some fuel injector cleaner additive and that minimized the problem immensely. Is this temporary drop in rpm's with lack of pressure on the gas pedal probably the fuel injector in dire need of professional cleaning? or is it something else entirely. has anyone else had this problem with their volvo? any help would be greatly appreciated for this new brick driver!!!

HI; It may be your IDLE AIR CONTROL VALVE is worn out. This valve compensates your air flow to the intake manifold just past the throttle body. Try this . Let it idle or have a partner keep it idleing around 1000rpm's ,then tap on the body of the idle air control valve and see if there is a change in your idle speed . If so you need a new one. It is located just under your intake manifold about half way down the engine block and in the middle of the block on the drivers side. Make sure the trans is in nuwtral. It costs about $110.00. Good luck. PS. check your wire connections first. Thanks; Dan...
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Dan's 88 Volvo 740 GLE WAGON non-turbo

Before you buy a new IAC, try cleaning the old one with some carb cleaner. Take the IAC out, and spray the valve end. It is also possible to disassemble and clean the electrical side of the assembly, but that's a little trickier. See the FAQ for more info on the IAC and rough idle.

If the IAC is fine, it could also be that the car is missing tach pulses from the Hall-effect sensor in the distributor. The little connector on the side breaks, leaving the cable dangling by the little wires, which in turn chafe and short out intermittently. Quick test is to gently shake the distributor harness and see if the car misses/dies. Pull the dist. cap and have a look, or pull the distributor for a closer inspection.