Volvo: 89 Volvo 740 Turbo Idling Question, fuel pressure regulator, vacuum leaks

Question
QUESTION: Heya Ray;

Quick question for you, I'm working on a 89 Volvo 740 T and am coming across an issue.  Right now when I run the car, the car idles fine, but after a minute the RPM starts dropping and then surging back up usually until the point that the car dies.  Fire it up again and starts fine without a problem for a minute.  I've replaced the Fuel Pump Relay, the InTank Prepump, the Fuel Pressure Regulator, and fixed an issue where the ECT and the Knock Sensor were flip-flopped.  Was wondering if you had any advice on what to try next, I don't want to get rid of the car (130,000 original miles) but I don't want to throw tons of money at it.  If you need any pictures or more details please do not hesitate to ask, Thanks!

ANSWER: Joshua,
If you are sure that all the bascis are right, like timing set properly and no vacuum leaks, clean throttle housing I would try a known good MAF sensor.

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QUESTION: Here's a question, for the MAF I noticed there was a different part number from the 89 Turbo to the 90 Turbo but the wiring and connector is the same.  Can they be interchanged?  If not, do you know of a good way to test the MAF?

Thanks for all of your help!

ANSWER: Joshua,
Use the BOSCH numbers stamped on the unit 89 should be last three 007 and the 90 016 not the same, different fuel systems.

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QUESTION: Sorry for such the late reply.  I had to acquire the MAF :)  I tried it out and the symptoms remained the same.  I noticed it is consistent throughout the range, although it tends to stall out in reverse more often.  I don't know if this makes a difference, but when I cleaned the throttle body, I saw there were two vacuum lines running to the Charcoal cannister.  One (Larger Hose) was plugged into the Charcoal canister, while a smaller one was hanging free. Should this be attached to the canister as well?

I'm struggling hehe.  I also tested the resistence of the MAF, and no matter which one I plug in, my resistence is at 3.1 Ohms, while Spec is 3.7, how big of a difference is this?

Sorry for all the questions, hopefully the details help a little, if you need more info please don't hesitate to ask.

Thanks!

Joshua Haber

Answer
Joshua,
There are two hoses to the Canister. I have seen these fall off before and there were not any symtoms. Since the symtoms remained the same go over the bascis again, something might have been overlooked. Check the fuel pressure and the regulator for leakage, the timing, the belt position also. Look for vacuum leaks, turbo/intercooler hoses, turbo bypass valve if appicable. Do these before seeking some help from a Volvo tech. The difference in measured values is nothing to be conserned about.