Should we be be changing sensors/parts prematurely?

[S2G-Unit]

All of my servicing & maintenance is up to date on my car. I've seen these part numbers come up on occasion in other threads. With the age of our cars, would you guys recommend we change any of these parts prematurely?


Front Bumper Air Temp Sensor SENSOR ASSY., AMBIENT - 80520-SL0-A01
Sensor Assembly, Air Temperature - 37880-PE2-013
Valve Assembly, Fast Idle (AF24A) - 16500-PR7-A00
Sensor Assembly, Water Temperature - 37870-PJ7-003
SENSOR ASSY., RADIATOR FAN CONTROL - 37760-PH7-003
VALVE ASSY., ELECTRONIC AIR CONTROL - 36450-PR7-A01
Thermo Unit (Denso) - Acura 37750-PH2-014

 

[Honcho]

All of my servicing & maintenance is up to date on my car. I've seen these part numbers come up on occasion in other threads. With the age of our cars, would you guys recommend we change any of these parts prematurely?


Front Bumper Air Temp Sensor SENSOR ASSY., AMBIENT - 80520-SL0-A01
Sensor Assembly, Air Temperature - 37880-PE2-013
Valve Assembly, Fast Idle (AF24A) - 16500-PR7-A00
Sensor Assembly, Water Temperature - 37870-PJ7-003
SENSOR ASSY., RADIATOR FAN CONTROL - 37760-PH7-003
VALVE ASSY., ELECTRONIC AIR CONTROL - 36450-PR7-A01
Thermo Unit (Denso) - Acura 37750-PH2-014

Many of the sensors on the car are simply resistors that vary current (typically 0-5v) based on the measured input. Resistors and electrical connections can fatigue over time due to heat cycles and corrosion, so my philosophy is to replace them with fresh units. Since I have to tune my car, I want to have fresh sensors- especially the TW sensor- to ensure the ECU is getting the most accurate data possible. So many fueling parameters in the ECU depend on engine coolant temperature. I'd replace all of your list except the EACV, since it is a solenoid and likely is either good or bad. That way, you're getting another 20 years of trouble-free sensors.

 

[Old Guy]

First off, if you have an OBDII car (doesn't apply to the OP of Honcho's project) you can check on your engine sensor status with a scanner. If the sensors are running within the limits specified in the service manual I would not mess with them.

For temperature sensors they are technically not a resistor; but, a thermistor. Thermistors tend to be less expensive than true resistance sensors (some of which use platinum) and generally have a higher temperature coefficient than resistor based temperature sensors so give more 'output' for the same temperature change. Thermistors are typically made from powdered metal oxides (think ceramic like) so tend to be dumb ass reliable. If there is an ageing problem with them it is the electrical connections to the device where the increasing resistance can cause a skew in the results. Be careful with the wiring and use conductivity enhancing grease / deoxit (do not use dielectric grease) on thee connections if you ae going to mess with them.

If you want to replace stuff, in terms of thermistors the one that has the most potential impact on engine operation is the manifold air temperature sensor. They are prone to fouling with EGR and PCV crap. Cleaning with brake cleaner usually does the trick; but, replacement would also do the trick. Be aware that thermistors can have a somewhat loose manufacturing tolerance (Honda does not specify the range on their device). Because the MAT has an impact on fuel mix it is possible that its replacement may cause the fuel trims to be off. Note that the air temperature correction in the fuel equation is based upon absolute temperature so small drift errors in the sensor normally won't have a huge effect.

There are a bunch of sensors that the OP has not identified that are much more mission critical. These include the MAP sensor, EGR lift potentiometer, throttle position sensor, O2 sensors, VSS, crank/cam position sensor ..... and I am sure some others. If you start replacing these on a preemptive basis things are going to start getting really, really expensive - particularly if you have a DBW car where a new TPS comes with a complete new throttle body if you do replacement as per the service manual. Older crank / cam position sensors can look like absolute merde; but, I have not heard that there is anecdotal evidence to suggest that they have an accelerating failure rate. That said, on an older car if a nice clean sensor makes you feel good replacement of that sensor might be logical when you are doing a TB replacement.

A lot of these sensors are difficult to get at with the engine in situ. If you ae not careful, you can damage the wiring during replacement which then becomes a double sized headache to fix. If the sensors are not a problem, I personally would not replace on a preemptive basis.

The sensors associated with the climate control I would leave to replace on confirmed failure as they are not mission critical.

ABS wheel speed sensors can be subject to mechanical damage from road debris; but, otherwise tend to fall into the dumb ass reliable category. If they fail it is typically due to damage where the wires enter the sensor body. They don't drift. They are usually good or dead - no in between.

I have not heard of a lot of issues associated with the coolant temperature sensors; but, I do recall that a couple of years ago owners on older cars were reporting problems which were traced to the fan control unit. Fan operation is a fairly important function. I seem to recall that some of these problems were attributed to solder joint failures similar to the main FI relay failures. You can decide whether you want to have a replacement fan control unit on hand or examine and reflow the connections.

 

[goldNSX]

I'd change none of them. Why? After nearly 30 years and over 200'000 km, some with a 'hot' CTSC, not a single sensor failed (except for the oil pressure sender unit which would be the only one I'd change because it can leak oil). I've been hunting down some gremlins, so I've checked and changed sensors but it was always another cause. It was a damaged injector base gasket, bad air.
Last weekend, I've checked the AIT sensor and it was perfectly within specs from -10 deg C up to 100 deg C. Warning: the deg. C scale in the SM is misleading, use the Fahrenheit scale.

 

[S2G-Unit]

Bumping my old thread.

Last year, I only drove maybe, 2000-5000km's. I had a broken windshield & it took I think 3 months to get a replacement.

After parking the car, I forgot to put on my battery tender, the battery died & needed to be boosted. Once boosted, I let the car idle for a few minutes then took it for a drive. At a red light, the rev's dropped a little bit & the car died. I gave it a few seconds & started the car again and made it home. I charged the battery for a few more days, started it, then let car idle & it died again in my driveway after probably 10-15 minutes.

The battery was replaced in June of 2020. Alternator was replaced prematurely in 2014. I'll need to have the battery & alternator tested.

Wondering what else to look at after the alternator & battery are tested when the snow melts here? I do believe I saw a post of some people resolving idle issues by changing these?

Honda 16500-PR7-A00 - VALVE ASSY., FAST IDLE (AF24A)



Honda 36450-PR7-A01 - VALVE ASSY., ELECTRONIC AIR CONTROL

 

[Old Guy]

If you can restart the car, I expect that the battery is OK and the alternator may also be OK. When you are driving down the street, give a quick look at the voltmeter. If it is above 14 volts, 14.5 would be nice, your alternator / charging system is probably doing its thing correctly.

Since you are talking about the EACV, I am guessing you do not have a drive by wire car. The EACV could be the problem and cleaning it might fix that problem, or not. The ECU also needs to go into idle control mode and there are a number of electrical inputs that it has to see before it engages the EACV. Based upon your description, I expect that it is not the fast idle valve.

Cleaning the EACV is low cost so give it a try. This would include cleaning the passages in the throttle body. Before you consider replacement of the EACV or fast idle valve get a copy of the service manual and check out the section in the Fuel Section covering the idle control system. There are a bunch of checks and tests (including testing those electrical inputs) you can do before you come to the conclusion that the EACV or fast idle is the problem.

Test and diagnose before replacing.

 

[S2G-Unit]

Thank you. Not to throw money needlessly away but if I were to buy those sensors, do they come from Honda already setup? Any adjustments need to be made? I believe I saw that one the sensors I had listed above required adjusting a screw for idle?

 

[Honcho]

In addition to the good advice above, I have an idea what might be going on. The 91-94 NSX has two key idle air passages that maintain a stable idle: the EACV and the idle set screw. Because of the PCV and EGR system design, these passages will both become clogged with oil blowby and exhaust soot.

The key for me was when you said you started the car, let it idle and then it died after about 15 minutes. Here's what I think has happened: the EACV and idle set screw are likely heavily clogged. When the car is cold, the FITV opens up and provides extra air to help the car warmup faster. It likely was providing enough air to keep the car running during this time. Once the FITV was closed, the car had to rely on the EACV and idle air passage, which could not deliver enough air to keep the car running.

Before spending $$ replacing stuff, I'd clean the EACV, its screen, the throttle body idle passage and the idle air screw.

 

[S2G-Unit]

In addition to the good advice above, I have an idea what might be going on. The 91-94 NSX has two key idle air passages that maintain a stable idle: the EACV and the idle set screw. Because of the PCV and EGR system design, these passages will both become clogged with oil blowby and exhaust soot.

The key for me was when you said you started the car, let it idle and then it died after about 15 minutes. Here's what I think has happened: the EACV and idle set screw are likely heavily clogged. When the car is cold, the FITV opens up and provides extra air to help the car warmup faster. It likely was providing enough air to keep the car running during this time. Once the FITV was closed, the car had to rely on the EACV and idle air passage, which could not deliver enough air to keep the car running.

Before spending $$ replacing stuff, I'd clean the EACV, its screen, the throttle body idle passage and the idle air screw.


View attachment 178359

I believe I have that filter in my parts box already. I think I ordered it when I started this thread. I'll take it out, thanks.

 

[Old Guy]

There is a procedure in the service manual for testing and setting the base idle speed. Whether you clean or replace your EACV you should go through the test part and if required do the setting part. With luck it will test out fine and no further fiddling is required.

 

[S2G-Unit]

I just started my car, It started just fine. As I sat in the car, after a few minutes the car died. I turned the key in the ignition & checked the voltage on the dash. The battery seemed fine above 12v.

I started the car once more & it has been running fine for about 15 minutes with the voltage is about 15v on the dash. I gave the car light revs which is what I did last year to prevent it from dying.

I came back to the car after about 20-30 minutes & it died. So I will start investing with I guess, the EACV and cleaning the filter?

 

[Honcho]

I came back to the car after about 20-30 minutes & it died. So I will start investing with I guess, the EACV and cleaning the filter?

I'm fairly certain that's your problem. The FITV is wide open on a cold start, so you're getting plenty of air. The car takes about 15 min to fully warm up at idle (assuming a good Tstat), which is where the FITV would close, so it seems to line up with your issue.

You should clean the EACV screen and the throttle body idle air passage. Both provide idle air during warm operation.