[Bikemark]

I have a '93 Previa, 225,000 miles that has started to stumble at idle. In cold weather (0 - 35f) it does not want to stay running at all. The Mass air flow sensor was replaced with a used item about 6 months ago, I belive that the fuel filter was done @the same time. My fuel mileage has dropped by 3-4 MPG at the same time. Any Ideas?

More Updates:
I have OK power once It shifts out of low.
If the air temp is above 45f The idle is better
If the Humidity is high the idle is low
The fuel filter was not the problem
Plugs and wires are less than 4 months old
I took it to the dealer, and of course it ran perfectly

 

[gideon1331]

I had that problem with my Corolla about a year ago and my Mom did with her Avalon (220,000 miles) just recently and a good cleaning of the intake manifold solved the problem. Gunk will build up around the butterfly air valve and it is not able to precisely meter the air when the valve is closed at idle and the engine will stumble. As preventative maintence my Dad cleaned his manifold. He said it was a little hard to reach but that there was a noticable difference at idle afterwards.

For the cost of a can of cleaner and a used toothbrush its a cheap way to try and remedy the problem.

 

[her94previa]

for two times I had a rough idle on my '97
1st- had to do with spark plugs and cable
2nd- too much air was going thru the MAF sensor

 

[her94previa]

Sorry, didn't get to finish my reply
How was my MAF sensor getting too much air?
Well, a field mouse somehow tunnel his way up into my air box and nipple at my air filter (about 1 " hole)
Couln't believe that shi.
The computer gave me trouble codes for these problems, you did not mention if your check engine light is on.
good luck.

 

[Bikemark]

More info on stumbling idle

OK, Here are some more clues to this puzzle.

• The throtle body bore was completely clean - no carbon, no gunk
• No check engine light
• The O2 sensors were replaced about 6 months ago
• The stumble is worse in drive than in park
• I cannot find any holes in the intake tract

I am going to replace the fuel filter now, it is several years old.

Any other possibilities?

 

[toyomoho]

Is the problem limited to just idle. Does the car drive OK and have the usually power?

 

[humanoid]

threads merged

 

[G. Ling]

Hi,

Did you get your cold weather stubling idle problem resolved yet? There doesn't seem to be any suggestions for problem solution.

I have a 03' AWD Previa with the same problem and would appreciate any suggestions.

Thanks.

 

[rickrolla]

Ok, Previas have both cold start injector system and a fuel pressure up system.

The cold start injector system consists of the cold start injector (located on the intake manifold), the start injector time switch (located below the coolant temperature sensor and coolant temp sender on the right front corner of the engine) and the ECU located under the driver's seat. The cold start injector adds extra fuel to the intake air to make starting easier. To prevent flooding, the injection time is limited by the time switch and a timer in the ECU. The ECU can operate the injector for up to 3 seconds regardless of the status of the time switch. If the coolant is above 113'F (35'C) the cold start injector will not work. Problems can be: Clogged injector, malfuntioning time switch, malfuntioning coolant temperature sender, defective wiring or ECU.

The fuel pressure up system consists of the fuel pressure regulator, the vacuum switching valve, vacuum tubing and the ECU. This system ups the fuel pressure for the first 2 minutes after starting to increase fuel flow by opening the manifold (Vacuum) refernce line to the atmosphere. If the vacuum line is clogged your fuel pressure stays high, using more gas. If your VSV does not work, you get less fuel pressure than needed for cold start.

Check your vacuum hoses and tubes to make sure they are in the right places and not clogged. There is a diagram under the hood or on the access panel under the driver's seat

Check your throttle position sensor. If it is loose or broken, it will cause an unstable idle. Previas are known for breaking the wires to the TPS. I extended the wires on my 92.

Good Luck

Rickrolla
92 Previa 5Speed 329,000km
91 Corolla Wagon 448,000km

 

[cato47]

I would seriously suspect the EGR valve. They get cruded up bad, especially if you haven't had one with that many miles. Sometimes you can get by with taking it off and cleaning it by hand. Make sure you get down in the manifold with a piece of wire cable and route it out.
A good air compressor can help a bunch on both the valve and manifold. Good luck friend.

Rick Cato