My 1998 mitsubishi montero sport suv is chugging, stalling out at times when I'm at a stoplight, to where I need to put veh in neutral to keep going. sometimes when I go from park to drive you seem to hear a "clunk". I thought maybe I put in some bad gas. could this be a tranny problem. Thank You Susan

From what you describe you have perhaps two unrelated but easy and cheap to resolve issues: 1) where your vehicle wants to stall is due to an idle air control problem and 2) the tranny clunk is probably nothing more than low fluid level. 1) When a car is at idle the throttle plate is closed and a vacuum builds up due to engine suction in the inlet manifold. Without air your engine stalls. The idle air control (IAC) system can take two forms a) a solenoid operated valve sitting on a passageway around the throttle plate or b) a motorised gear mechanism that actually opens the throttle plate a tiny amount to allow air to bleed past it. IAC problems are also associated with sudden stall at start up when the AC is switched on or when you engage 'drive'. This is because the IAC is unable to make corrective adjustment to the amount of air required by the engine at these times. How to fix: Remove all the air ducting between the air cleaner and the throttle body, this is just to give you access. Using a cloth and WD40 or carb. choke cleaner spray clean the inside of the throttle body of all the black gunk. Clean the throttle plate out face, apply pressure to the top of the plate to turn it and then clean behind it, the edge of the throttle plate and the back of it the best you can. Check to see if there is a finger diameter sized passageway leading off the side of the throttle body interior just before and just after the throttle plate shut position. If there is such a passageway you will have the valve type control system (see above). The valve is held on to exterior of the throttle by a couple of bolts (10mm?). Disconnect the electrical connection to it and unbolt it. Clean the valve interior until like new paying special attention to the valve and valve seat. Clean the passageways on the IAC and on the throttle. Reassemble when spotless. If you do not find passageways on initial inspection then you have a motorised throttle opening system. Cleaning the throttle plate and interior will be enough. All this cleaning is to remove all obstruction to the small amount of air bleed. Refit everything taking car to make the air ducting connections properly. This should help solve the idle issues. If a problem persists check every 'vacuum' tube making connections with the inlet manifold or 'hissing' leaks whilst the engine is idling. 2) clunking in the transmission is usually due to low fluid. The transmission fluid dip stick is at the back of the engine. Only measure the fluid level when the engine is running (this pumps fluid to the torque converter and allows correct levels to be determined). You will need fluid of the correct type (consult with Mitsubishi). Add fluid at 500ml at a time via the dip stick tube to top up the transmission, check level between each top up. Once at correct maximum level refit the dip stick. All done

Your pcv valve needs to be replaced