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Poor MPG weird idle

898 views 11 replies 5 participants last post by  DREWZ AIRFLOW SE 
#1 ·
Well my 95 900set 5spd is getting really bad gas mileage. According to the sid 13.9. The car also has this weird idle issue where the idle sits at around 1100rpm and sits at 1500 when you come to a stop for a bit. The idle has also surged up to 3500 and stuck there before. I swapped out AICs today and it did nothing. Is there a way to test a AIC with a multimeter? This fuel economy is killing me. Most of my driving is in the city. My car is slightly modded. It has a 93 tranny, spec clutch, viggen PP, Saab Sport exhaust, viggen IC, poly motor mounts and BOV venting to atmosphere.


Anyone have any ideas?
 
#3 · (Edited)
Modifications and fuel economy do not go hand in hand..

Determine the real MPG by simply doing the math, this will may take a month to gather enough info for any accuracy , the downside...

Rather than "swapping" out the IAC, clean and service it; then test all the vacuum lines using your vacuum pump($25 at Harbor Freight)..

If the MPG were really that bad; one would think a CEL would be generated..

According to Haynes
IAC
number of coils ............2
coil winding resistance...9 to 15 Ohm
frequency.....................100 Hz
 
#5 ·
DREWZ AIRFLOW SE said:
could a fuel filter cause bad mpg?
No
But city driving in cold weather can... and does..
The engine should be warm at minute 4, hot at minute 6, if the t-stat is right..these are approximate times....
The fuel filter is another service item; change every 60K miles or so.
 
#8 ·
Ok I put some techron in the tank and did some adaptation runs the car runs a lot better now in general but the idle still sits just over 1k rpms.
 
#9 ·
The only time I had an idle over 1000 was when I changed my vacuum lines and forgot to re-connect the Throttle Position Sensor... But then again, my car wouldn't shift out of first gear (auto.)... I definitely think the car's getting to much air. Good luck!
 
#11 ·
Suggestions

How long have you owned the car and what preventative maintenance have you done? I have a '96 900S and am anal about keeping the car in good running order. When my 900S began to run poorly I began with the basics first and did a tune up since I didn't have any previous maintenance records. I did this:
1. Changed the fuel filter (the car was cutting out/ bucking when driving up hills).
2. Changed the fuel pump ( for the same reason as #1).
3. Cleaned the Air Induction Valve ( for the same reason as #1).
4. New Ignition Wires.
5. New Rotor & Distributor Cap.
6. Rechecked the new NGK spark plugs that were put into the car by the previous owner- they were the wrong NGK plugs. After I put the designated NGK's in the car ran fine.

Do you expereince any other symptoms than just the weird idle?
 
#12 ·
Ok I have owned the car for 3 years. I take care of it. The car is a turbo so no dizzy. I have to do the fuel filter I have one just need to get it into the garage. No space as of now. Plugs were done a few months ago as well as air filter and oil change. I do get a gas smell sometimes. I have a 9-3 fuel rail and FPR in the car.
 
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