Idle and start issues

[2.2TLegacy]

Got a couple of lingering issues that I am trying to hammer out with my build.

1. Cold Start

Car fires up quick (as it should) but rpm's shoot up to 2,500 and then slowly lower until the 'normal' 1,500 cold start idle. Is that a normal cold start idle progression? Also, how long is the cold start idle supposed to last? I experimented one morning and just let the car idle until warm up and it took about 10-12 minutes for the rpms to drop to below 1,000.

2. Cold and Warm Start (so like getting into after work or just running down to the store where it only sits for a few minutes)
So after the 1st start of the day, when I start the car the rpm's shoot up to 1,500-2,000 and then slowly drop until it gets down to warm idle. Doesn't matter if the car has been sitting for 5 minutes or for a few hours (obviously the longer it sits, the longer it takes to get to warm idle). So my question here is why do the rpm's shoot up so drastically, even if the car is up to operating temp?

Also, after the first start (where it starts quick as mentioned in #1) it take a bit of cranking to finally get the car to turn over. This is a recently developed issue (only the last few weeks or so). Before then the car would crank and start faster than my brand new VW ever does. So I am wondering what is causing the extra crank time before turnover.

Recent maintenance items:

- Coolant system drain/flush and refill
- All coolant hoses replaced
- Thermostat replaced (OEM subaru t stat)
- WRX metal coolant tank

[rallyak]

Coolant sensor? I believe that 90% of cold start issues is related to that one sensor. It pretty cheep and probably should be considered when doing a tune-up.

[2.2TLegacy]

That was one thing that i was considering. Can those be replaced without doing a partial drain of the coolant system?

[rallyak]

Yes, but you still need to burp the system.

[Turbo_Carl]

That was one thing that i was considering. Can those be replaced without doing a partial drain of the coolant system?

Very easy install.

When I bought my legacy I was able to get it for $400 less than the guy wanted because of the check engine light. I ended up paying $1600. I replaced the knock sensor and coolant sensor and haven't had an engine light since. I would recommend taking care of the knock sensor too while your back there.

I have only one warning.

BE EXTREMELY CAREFUL WHEN TIGHTENING THE COOLANT TEMP SENSOR.

I overtightened and broke one. Good thing they are fairly cheap.

[Legacy777]

The idle revs sound about right, but may be slightly elevated, which I agree I would probably look at replacing the coolant temp sensor. The revs and now the harder to start may be an indicator it's on the way out.

[2.2TLegacy]

Ordered a new coolant temp sensor, i'm going to install it on Saturday and i'll report back here afterwards.

[2.2TLegacy]

Replaced the coolant temp sensor, seems to have lessened the symptoms listed above, car seems to locate the 'correct' idle a bit faster than before.

Crank time is still a bit slow after the first start of the day.

[2.2TLegacy]

day 2 update. Car seems to have issues idling for anything over about 10 seconds at full operating temp. It will stumble down to 500, back up to 750-800, back down to 500 and then either stall out or ramp it back up to about 1200rpms.

Next on the list is probably checking the IAC valve for correct operation.

[Baddog]

I am experiencing the same issue. I was going to replace the coolant temp sensor and clean out the IACV.

Let me know what you come up with.

[2.2TLegacy]

Just decided to do an ECU reset. Seemed to have solved the issue for me.

[Legacy777]

I was going to suggest an ECU reset after replacing the CTS. Learned fuel & timing trims from bad sensors can be a real issue, so it's always a good idea to reset the ECU after replacing a suspect sensor.

Hopefully that fixed the problem for you and it will stay fixed.

[devilzdriver]

I was going to suggest an ECU reset after replacing the CTS. Learned fuel & timing trims from bad sensors can be a real issue, so it's always a good idea to reset the ECU after replacing a suspect sensor.

Hopefully that fixed the problem for you and it will stay fixed.

CTS replacement solved about 5 problems i was having between idle and startup 20$ part 2 min or replace totally worth it!