Cold start CEL P152D / P1561

[i_love_cars]

Greetings,

For the past year or so, I've been receiving the following CELs on cold starts I'd say 70% of the time:

P152D - Idle-speed control valve monitoring incorrect actual value (Bank 1)
P1561 - Cold start idle air control system RPM lower than expected (Bank 1)

The other 30% of my cold starts I don't throw codes but after cold-start sequence completes, the car increasingly ramps up idle speed towards the better part of 2000 rpm.

In all cases, without fail, 100% of the time, as soon as cold start sequence completes, all the car needs is to be shut off/turned on again and it immediately idles perfect, drives perfect, and the codes clear on their own.

The one oddity I notice on cold start is that after 15 seconds or so, there is a noticeable dip in RPMs to about 400-500. This only lasts for a second and then it pops back up, but often will trigger the CELs (which may make sense given the description of idle speed/RPM too low). I just don't know what would be causing it at this point.

I have 84k miles on the car right now and a few months ago I tried to fix this issue by replacing the usual suspects that the CELs would point to. I have replaced the following components:

1. Idle air control valve
2. Fuel tank breather valve
3. Secondary air pump
4. TAs (for good measure since I was in there anyway)

The car has an ESS625 with a canned tune, xpipe, exhaust and is otherwise unmodified in terms of the engine. The car has seen 15k+ miles over the last 4 years in this modified state with no problems. This particular issue only started happening last summer.

I'm looking for ideas on where else to look for problems because I've followed the CEL codes already and replaced the parts they would suggest but nothing has worked to fix the problem.

[NiBe]

What is TA? Does it on cold cold start meaning overnight or also on cold start meaning that lambda sensors are not heated to operating temperature aka after a let's say 15 minutes stop?

[i_love_cars]

Originally Posted by NiBe

What is TA? Does it on cold cold start meaning overnight or also on cold start meaning that lambda sensors are not heated to operating temperature aka after a let's say 15 minutes stop?

TA = throttle actuator

Overnight cold start is the issue. I can let the car sit for probably up to 8 or 9 hours before it gets cold enough to become an issue again.

[NiBe]

"the car increasingly ramps up idle speed towards the better part of 2000 rpm."

To me it looks like DME gets incorrect data from some sensor and tries to compensate a non-existing problem and the feedback after compensation is the same so it tries to compensate even more and more.

But to be honest I don't know what is the issue. ISTA typically suggests tests for each error code, there are many diagnostics tests which could theoretically provide some info.

Or take the car to a shop because like this you can spend a lot of money and move nowhere.

Btw did you do a vacuum/smoke test?

The question about overnight was to understand if it relates to engine being cold or lambda sensors not being heated (and thus engine operating in open loop). Per your answer it has nothing to so with lambda sensors.

You can also gather more diagnostics data. Charts of air flow/pressure, lambda sensors, STFT, LTFT, together with RPM when the issue is occurring, maybe you will see that some of them correlate and it could bring more light on the problem.