Hi all, I'm new here.

A couple months ago I picked up a very nice 1993 Volvo 240 wagon with 142K miles. My parents had one just like it in the mid 80s. I remember riding around in the rear facing seats. Good times.

So far I'm loving Volvo ownership. It's an easy car to work on. To give some more background, I'm a bit of a Subaru nut, 8 years and counting. I track (road course) my STI a few times a year. The STI has been sitting in the garage for over a month on a battery tender because I enjoy the Volvo THAT much. :)

The 240 had a few issues when I got it. The idle was rough and lumpy. It would stall occasionally. There were NOT any check engine lights. The check engine light does function, as it has come on after unplugging the MAF and O2 sensors.

So far I've done the following, which has improved the engine power and responsiveness, but hasn't cured the rough/lumpy idle:

- airbox thermostat replaced - it was stuck half way open so a mix of hot and cold air were entering the airbox. New thermostat confirmed to work post installation.
- airbox flapper cleaned and lubed - moves freely and easily now
- air filter replaced
- post MAF (AMM) tubing replaced with Volvo OE part- there was a crack.
- MAF (AMM) cleaned with MAF cleaner
- O2 sensor replaced with Volvo OE par
- PCV flametrap, filter, and hoses replaced with Volvo OE part
- PCV oil box (under the intake manifold) replaced with Volvo OE part
- FPR (fuel pressure regulator) replaced
- FPR vac line replaced
- PCV vac line replaced
- throttle body cleaned, throttle position sensor adjusted, gasket replaced
- ICV (idle control valve) cleaned
- Intake manifold gasket replaced with Volvo OE part
- Fuel injector o-rings replaced, pintle caps replaced with Volvo OE part
- spark plugs replaced with Volvo OE part
- spark plug wires replaced
- distributor cap replaced with Volvo OE part
- distributor rotor replaced with Volvo OE part
- oil + filter change
- oil cap seal replaced
- oil dipstick o-ring replaced
- odometer gear replaced (it quit on me a few weeks ago)
- seafoam'd via vacuum line (prior to oil change)
- techron fuel injector cleaner run through 2 tanks
- OE tachometer installed
- vacuum gauge installed

Within the last 10K miles, the previous owner had major work done at a local Volvo dealership:
- engine mounts were replaced before I bought the car, I confirmed that are still in good shape
- head gasket replaced before I bought the car. No burning oil or loss of coolant now.
- fuel filter replaced before I bought the car.
- front AND rear seals replaced on the engine before I bought the car.
- MAF replaced ~30K miles ago

The engine is VERY responsive now. No stalling or hesitation when I get on the gas. However, with the car in park or neutral, the engine has a bit of a shake. The shake isn't as noticeable when the car is in "Drive" (it's an automatic).

The RPMs are CONSTANT on the tach (750-ish). The engine pulls about 19 in/hg vacuum. I've been getting between 17 and 20 mpg in town.

I've been trying to track this issue down with no luck. As you can see, I've replaced LOTS of parts, but the engine still shakes at idle. It shakes as if there was a vacuum leak, but I've replaced the entire PCV system as the majority of the vacuum lines.

As I mentioned above, there isn't a check engine light. I've also run a number of the "self diagnostics" on the car and everything checked out fine.

Some potentially odd behavior is that the engine surges when I pinch the PCV vaccum hose (the hose from the flame trap housing to the intake manifold).

Another odd thing is the MAF has 6 pins, but the wiring harness only has 5 female connectors inside. Again, no CEL has been present. The CEL does come on when I unplug the MAF. I found another forum with a post discussing this, but there weren't any right/wrong definitive answers.

What gives? Is the lumpy idle normal?

Thanks!

- Mike

Some pictures: