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Old 04-20-06, 05:14 AM   #1 (permalink)
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Hesitation and poor gas mileage

I have a 1990 Acura Legend L coupe with 90,000 mi.

Awhile back, I noticed that it had hesitation problems but the gas mileage was normal (25mpg) so I thought it could be the O2 sensors.

After I changed both the front and rear sensors, I'm still having the same hesitation problem but now the gas mileage has dropped to 15 mpg.

I looked at the emissions testing results for this car before and after the O2 sensor replacement and everything stayed pretty much the same EXCEPT for HC. The HC was much higher (but still passed) when tested after the O2 sensor change.

I figure that if there's nothing wrong with the new sensors that I installed, then the hesitation problem is probably caused by something else.
The only major thing the previous owner changed was the timing belt @ 60,000 mi. (for regular maintenance, not defect).

Judging from what I described, can someone tell me what are the possible problem areas that I should at?
Where should I begin?

Thanks.
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Old 04-20-06, 05:46 AM   #2 (permalink)
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Check ECU for error codes. Behind top of carpet on pass. side footwell close to console.

Code 6 is coolant temperature (TW) sensor. Even if no error code, can still cause bad mileage (running rich).

A defective ECT (CTS or TW) sensor may cause some of the following problems:

Hard engine starting
Rich or lean air/fuel ratio
Improper operation of emissions devices
Reduced fuel economy
Improper converter clutch lockup
Hesitation on acceleration
Engine stalling


The TW sensor is often referred to as a CTS (coolant temp sensor) or ECT (engine coolant temp) by different people; TW is honda-acura term.

It is located under the distributor, has 2 pin connector on it, talks directly to engine computer (ECU), and is screwed into a pipe-thread opening.

Coolant temp sensors can cause a lot of weird idle probs, running rich, poor performance, shift probs, and starting probs.

$30 to $40 at auto parts stores.

Hope this helps.

Let us know how it goes.
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Old 04-21-06, 06:46 PM   #3 (permalink)
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Thanks for your help Dallas, I will definitely replace that to see if it works.

I just spoke to the dealer, and they told me there are 3 separate parts that make up the CTS:

1) sensor assembly $ 38.09
2) sensor assembly $ 61.47
3) 'A' thermo sensor - $ 45.23

I'm thinking the first two are not related but they want me to buy. The 'A' sensor appears to be the one you are talking about. I'm heading over there right now.

I'll let you know what happens.

Last edited by Mouse; 04-21-06 at 07:15 PM.
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Old 04-21-06, 07:40 PM   #4 (permalink)
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Dealer oughta know what the TW sensor is.

All you need is the 2-pin sensor that has pipe threads on it that screws in under the distributor. It is not a dealer-only item. Cheaper elsewhere. You don't need the others.

Not so far...

Last edited by DallasLedge89; 04-21-06 at 11:02 PM.
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Old 04-22-06, 04:18 AM   #5 (permalink)
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Did you check the ecu as Dallas state? There also may be a yellow LED flashing meaning a poor idle. When does this hesitation occur?
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Old 04-22-06, 11:49 PM   #6 (permalink)
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Hi 88,

Yes I checked the error codes like Dallas said but there weren't any. The red light just flashed once and no amber light flash when I turn the ignition key to ON. I think that's normal and not part of the code.

At this point, I don't know what I'm going to do. The TW sensor is $ 61.00 at the dealer and he said it takes a few days to special order it. Dallas: I'm wary of auto part store stuff, better to spend a few dollars more for peace of mind.
Right now I'm having my doubts. If I change the TW and it turns out to not be the problem, then I've guessed wrong again.

Btw, since the two new O2 sensors I installed didn't help and only made things worse, I think they may be defective. Should I put back the two original ones or should I buy two more and take my chances that these will turn out good?

What brands do you guys recommend? I bought them online and they were made by Denso. There's another brand that I think is good, it's NTK.

I'm just so confused. The gas prices is going through the roof and my car decides this is the time to start burning up gas.
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Old 04-23-06, 01:30 AM   #7 (permalink)
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Don't replace the TW if you don't know for sure thats your problem and the first flash i don't believe is supposed to happen so watch the ecu as your car warms up ALL the way and see if any codes occur (15-20min idle-5 or so driving) because at full warm is when most codes will occur.

Also when does the Hesitation occur?
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Old 04-23-06, 01:31 AM   #8 (permalink)
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I've already given you the answer you need. If you don't believe it, use the forum 'search' function. You'll have to sift thru 200 or more posts, because there are a lot of rather less than helpful posts, but ultimately you'll get the same answer I gave you up front.

The functional specs for Legend oxygen sensors are the same. In fact, the same sensor works on a huge variety of cars, only the connectors are different. Personally, Bosch universals are cheaper, and work fine. My current coupe is not my first Legend, and the Bosch sensors have done fine.

And the chances of your new sensors being defective are about the same as you winning the lottery, and being struck by lightning on the same day.

Lastly, oxygen sensors usually fail gradually, they don't set a code till they are completely non-functional. The same is true for TW sensors... they are thermistors (semiconductors), and like any other semiconductor, they can get flakey with heat, use, and age. Changing O2 sensors and having a flakey TW sensor can very well make your gas mileage worse, since the ECU is no longer running in backup or fail-safe mode, and is trying to use sensor input again. It is, after all an 8-bit computer from '89 or '90, and does not make the 'finer distinctions' that a newer car's ECU does.

The TW sensor, and the two O2 sensors are an electronic fuel injection system's 'holy trinity', on any modern car. All three must work properly for good performance and gas mileage.


Last edited by DallasLedge89; 04-23-06 at 01:53 AM.
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Old 04-23-06, 02:10 AM   #9 (permalink)
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Actually, 88, that single brief flash is the "I'm alive and operational" signal from the ECU, according to the factory service manual. Mine does it and so does yours if you are looking at the LED port and turn the ignition on at the same time. If it doesn't happen then you do have a problem.
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Old 04-23-06, 05:03 AM   #10 (permalink)
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Quote:
Originally Posted by DallasLedge89
Lastly, oxygen sensors usually fail gradually, they don't set a code till they are completely non-functional. The same is true for TW sensors... they are thermistors (semiconductors), and like any other semiconductor, they can get flakey with heat, use, and age. Changing O2 sensors and having a flakey TW sensor can very well make your gas mileage worse, since the ECU is no longer running in backup or fail-safe mode, and is trying to use sensor input again. It is, after all an 8-bit computer from '89 or '90, and does not make the 'finer distinctions' that a newer car's ECU does.
The TW sensor, and the two O2 sensors are an electronic fuel injection system's 'holy trinity', on any modern car. All three must work properly for good performance and gas mileage.
You have a good point there. You know what, I think I'm going to do it and change the TW. I mean, what's the worst that can happen? It's only $61, it cost more than that just have them diagnose it and they say can't guarantee of finding anything!

Is the TW hard to remove and install? I think I found it today and it's in a very tight space where you said it would be, underneath the distributor, slightly towards to the back.
Does the threads need a special lubricant like the O2 did?
How long do these TW's last anyway?

@88
I guess I should've elaborate more on the hesitation. It happens when I accelerate. Another thing that always happen besides the hesitation is these slight "jerks" (no, not the people but the motion) that always seem to occur when I accelerate to @ around 5 mph and again around 20 mph and I think again somewhere in the 40's.
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Old 04-23-06, 05:56 AM   #11 (permalink)
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Another example from down under...

Just another post

Just get a wrench on it. Tapered pipe thread. New one comes with sealing compound on the threads. Don't torque, just snug it (pipethread is not like a bolt).

And they probably last even longer today than the ones made when these cars were new, considering how much better the technology is today. An auto parts chain here called O'Reilly's has OEM-grade temp sensors made by Borg-Warner (major OEM manuf.) for $40 with a lifetime guarantee. Can't beat that.

Wouldn't steer you wrong, friend.

Oh, and your elaboration on the hesitation? Classic TW sensor symptom. Check the aussie link above. I told him the exact same thing. No code 6 error on his ECU, but does have 1 quick blink. Just like yours... how 'bout that?

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Old 04-23-06, 07:58 PM   #12 (permalink)
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I just ordered the part from an online dealer, DelrayAcura (acuraoemparts.com) for $44 plus $8 (s+h) = $52 total.
The local parts store here don't have a very good selection and their prices aren't that much better.
Ground shipping will take a good week, so I'll be putting this thing in the 1st week of May.
I can't wait.
Thanks fellas, I'll let you know what happens.
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Old 06-13-06, 03:26 PM   #13 (permalink)
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Mouse,

did the TW sensor fix the problem? I'm interest because I've been experiencing the same problems and have tried pretty much everything you have to no-avail.

Let us know!
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Old 07-11-06, 03:57 AM   #14 (permalink)
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Sorry walkingthemile, I haven't check this forum for a while now so I didn't see your post.

Anyway, I was able to replace the TW sensor and it help the hesitation somewhat but the slight tug or jerky motion (different from hesitation) I get when I accelerate is still around. It also did not get rid of my poor mileage.
However, don't go on what I experienced and assumed it's the same for your car, you should still try to replace the TW sensor.

I really believe my problem comes down to the new O2 sensors I installed. I suspect they might not be good because it's only after I installed them did my gas mileage dropped (from 25 mpg to 15 mpg). I'm looking to get two new ones (different brand and from a different retailer) and replace them again.
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