Hi all, this is my first post on this site. I'm young but I've owned two Volvo 740's and i'm slowly becoming familiar with everything.

Yesterday, my girlfriend was out driving my 91' 740 wagon and told me the red Brake light came on indicating low brake fluid. I filled it up to the correct point and also noticed she lost my gas cap for my tank (no tank door). I quickly got a new one and thought my car would run great like it has been, I'm a pizza delivery boy and drive my car often and it's been amazing.

Occasionally, starting the car it would take a few seconds to turn but usually just needs some gas to stay on and it's fine. But now I've noticed bad idling with it. When I start her up I notice how shaky the car and engine is and it idles roughly at about 800-900 RPM in park. When in gear the RPM drops to a rough 500-600 count and feels very weak and shaky.

From what I've seen on the net I was told to check my plugs/ any leak in them, the IAC (Idle air control valve, but car always starts fine regardless of weather), the RPM sensor or crankshaft sensor and any vacuum leaks. The plugs are completely fine, clean and wired correctly. I'm not sure where or how to check the IAC or the sensors. Granted i'm a noob at any car mechanics as well. I'm a young kid with a low paying job and low budget so I was wondering if there is anyway I can check to see exactly what's wrong with the bad idle. I've put in a new fuel pump relay, plugs, new ignition switch, and fuel pump/ filter.

Any ideas on on the next step I should take? I need my car running smoothly because I use it everyday.

 

air leaks anywhere between the MAF and the cylinder head can cause all sorts of bad running.

is this a bosch LH2.4 or regina rex system? bosch uses a mass airflow sensor, while regina uses a manifold air pressure sensor. regina systems also have a different ignition system, which uses a square 'transformer' style ignition module/coil, while Bosch uses a standard 'beer can' ignition coil, with a separate ignition module on the left fender wall.

and, um, you may just need a basic tuneup, new spark plugs, distributor cap + rotor, and possibly new spark plug wires. you want to use simple copper plugs, not any fancy platinum or iridium or whatever. NGK BPR6ES or Bosch W7DC, or the Volvo branded plugs that come in a set of 4. The ngk and bosch plugs I specified come with a removable tip, depending on your spark plug wires, you may need to remove the sleeve and the wires will grip the threads directly.