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2,5 warm engine hesitation


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This issue has been evident, I think, since I bought the car. Now before a smartass comments the 2,5 will be hesitatious all the time, I will describe it.

 

When the car is cold, like the first mile, the engine feels more frugal from low revs, up through the gears. I never rev more than 3000 on a cold engine, so I wouldn't know if there is a difference further up.

 

Some times the engine seems to swap between two "modes" during warmup, resulting in the tach alternating slightly (300-400 rpm) during acceleration. During these occasions there is a most evident (well my wife wouldn't notice :whistling: ) power difference.

 

With the engine warm, I sometimes find it hesitatious way up in the revband, at least up to 4500 rpm. Other times it is acceptably frugal from 3500 and up.

 

Any idea what this might be? I've never had the codes read, and I obviously have no check engine light as my Xedos don't have any. My milage has always been great, up to 33,1 MPG.

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It is normal for an engine to be a little sluggish when very cold, even the new ones I rent. Especially when it is -25 deg C and below. Very often they rev high when started, then they seem to bounce down gradually until the engine is at operating temp.... AS for the hestitation at the higher band, I know is seems simple but when is the last time you checked the filters (AIR & FUEL)?

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Now my engine is more powerful on low revs when cold...

 

My filters are clean, obviously you're into an important thing to check though, my K&N airfilter clogged up during sommer enough to make my KL hesitatious around the maximum torque area, 4500 to 5000 rpms. Easily diagnozed and fixed.

 

I myself have leaned towards

 

1. VRIS malfunction, but they seem to be operating like they should, at least they open and close both of them, haven't checked if the rpms are correct though.

 

2. Would it be worth a try to reset the ECU by disconnecting the battery etc, maybe the ignition timing has been set back more than it should by the knock sensor?

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Hold on, your engine feels MORE powerful when cold? That's a new one. To check if the VRIS is opening, put a piece of paper on the solenoids where they contact the studs (when VRIS is closed). Wow, it's actualy quite hard to explain what I mean. But, with the engine not running, push on one of the valves so that it opens a little, and put a piece of paper in between the triangle part, and the stud that it's pushed up against when closed. Do this for both valves. Now go for a spirited drive. Once the fun has ceased and you're back in your driveway, pop the hood and see if the pieces of paper are still there. If they are, then something's wrong with your VRIS. If they're gone, then VRIS is working. I would lean toward a faulty IAC, or temp sensor before going with the VRIS.

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Thanks Ren, actually I've already checked the VRIS solenoids, they are easily checked by flipping the hood and just revving the (warm) engine north of 7000 rpm while looking at them, they also make a significant clicking sound when engaged. But thanks for your guide anyway. They're both supposed to close north of 7000 rpm, hence the spirited driveway procedure lol.

 

I'm not talking about freezing cold engine, more like 0-15 degrees C. Actually the occasions when it sort of alters between two "modes" has made me aware of it as in maybe being an issue.

 

What is IAC short for? And will a faulty IAC or temp sensor (on the air filter box right?) trig a code? It IS possible to read the codes on my car as well. There just isn't a check engine light.

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Either one will trigger a code.

 

IAC - Idle Air Control valve, located on the bottom of the throttle body. Usually when faulty it makes the idle somewhat irradic. But it works based on the temperature of the engine, so it's definitely a possibility.

 

See if you can get a code pulled, that would be the best place to start.

 

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all cars feel different in the cold then in the warm, generally a cold engine may not feel as powerful since the oil is so cold, however, usually its the transmission that feels quite different

 

No, generally the car feels less powerful, from the cold oil and transmission warming up. The only time the cold makes the car feel more powerful is when the tranny is warmed up and you drive long distances into the night, the car may be warmed up, but ends up sucking in air 20-30 degrees cooler then when you first started.

 

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Could be dead o2 sensors. When the engine is cold it runs rich in open loop, causing greater power. But as the engine warms up, it leans out and goes into closed loop. If the sensors are relaying the wrong info, it could be running too lean causing a lack of power. Just a thought.

 

And again, see if you can get some codes pulled.

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