Strange Idling Behaviour (FC)
08-03-16, 08:14 AM
#1
Rotary Freak
Thread Starter
Strange Idling Behaviour (FC)
I recently purchased a 1986 RX7. It has had a new engine swapped in, and there are about 10,000KM on the engine.
When I turn the key, the engine starts up very quickly. and the tachometer indicates that it goes to 3000 revs, then goes down to 1000 over the course of one second. It then sputters, stalls, and dies (as if it is not receiving adequate gasoline). If I start it and idle it manually using the gas pedal, after about a minute to minute and a half of warm up time, it will hold an idle between 750 and 800. It then idles indefinitely without any major issue, although the idle is a bit lumpy and seems to float about more than it should. Also, even when it is idling properly, if I activate the AC compressor the engine stalls and dies.
So, originally I had believed this was a dirty throttle body issue. Now I'm thinking the BAC valve may also be dirty. Before I remove either part for cleaning, I wanted to see what other people thought about the issue.
P.S: I do have a can of Seafoam which I will dump into the gasoline at some point. I don't believe it will have any effect on the idle issue, but the injectors could use a good cleaning anyways.
When I turn the key, the engine starts up very quickly. and the tachometer indicates that it goes to 3000 revs, then goes down to 1000 over the course of one second. It then sputters, stalls, and dies (as if it is not receiving adequate gasoline). If I start it and idle it manually using the gas pedal, after about a minute to minute and a half of warm up time, it will hold an idle between 750 and 800. It then idles indefinitely without any major issue, although the idle is a bit lumpy and seems to float about more than it should. Also, even when it is idling properly, if I activate the AC compressor the engine stalls and dies.
So, originally I had believed this was a dirty throttle body issue. Now I'm thinking the BAC valve may also be dirty. Before I remove either part for cleaning, I wanted to see what other people thought about the issue.
P.S: I do have a can of Seafoam which I will dump into the gasoline at some point. I don't believe it will have any effect on the idle issue, but the injectors could use a good cleaning anyways.
08-03-16, 09:10 PM
#2
If you've not read Aaron Cake's Ground article (Google it), do so and follow it to the letter. It doesn't necessarily sound like a ground issue per-se, but a poor ECU ground can result in all sorts of issues that masquerade as other ailments.
An added benefit is that it will guarantee that your throttle position sensor can have its full range available.
Does this behavior occur on cold out hot starts?
An added benefit is that it will guarantee that your throttle position sensor can have its full range available.
Does this behavior occur on cold out hot starts?
08-03-16, 09:31 PM
#3
Originally Posted by Akagis_white_comet
If you've not read Aaron Cake's Ground article (Google it), do so and follow it to the letter. It doesn't necessarily sound like a ground issue per-se, but a poor ECU ground can result in all sorts of issues that masquerade as other ailments.
An added benefit is that it will guarantee that your throttle position sensor can have its full range available.
Does this behavior occur on cold out hot starts?
An added benefit is that it will guarantee that your throttle position sensor can have its full range available.
Does this behavior occur on cold out hot starts?
08-14-16, 06:24 PM
#4
Rotary Freak
Thread Starter
Fixed (or rather, improved)
I fixed my idling issue. The first things I did were redo the grounds as per Aaron's article (thank you Aaron, by the way). I was actually in the process of doing this when you guys suggested it. It didn't improve my idle issue at all, but did fix a different problem with my seat belt light going off at random.
Next I tightened some vacuum lines, which seemed to make idle a bit more stable, but didn't fix my cold start problem.
The last thing was I cleaned the contacts and wiggled the connector on the temperature sensor connected to the cold start system (I don't know how else to describe it, it's near the TPS), and this fixed the problem immediately. It seems the problem came from the engine running lean on cold startup due to the temperature sensor being disconnected, and the ECU defaulting to warm start up.
The idle is still lumpy, and unstable when I activate AC or other peripherals. Next, a throttle body / BAC valve cleaning should be in order.
Thank you all for your input! I appreciate the help.
Next I tightened some vacuum lines, which seemed to make idle a bit more stable, but didn't fix my cold start problem.
The last thing was I cleaned the contacts and wiggled the connector on the temperature sensor connected to the cold start system (I don't know how else to describe it, it's near the TPS), and this fixed the problem immediately. It seems the problem came from the engine running lean on cold startup due to the temperature sensor being disconnected, and the ECU defaulting to warm start up.
The idle is still lumpy, and unstable when I activate AC or other peripherals. Next, a throttle body / BAC valve cleaning should be in order.
Thank you all for your input! I appreciate the help.
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