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Idle issues

Old 07-07-18, 03:24 PM
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Idle issues

Hi, I have a '93 with a single turbo t78 and a power fc, running the oem secondaries as primaries. It started and ran fine for several years, but then I let it sit a while. After a lot of work it starts readily now. It starts pretty much immediately, and climbs up to ~1500rpm. After just 1 or 2 seconds it rapidly drops and barely recovers typically around 400-500 rpm, it climbs back up to around 1200, then drops again and usually stalls (always stalls after a second dive). I can hear the IACV opening up and air flowing (sucking sound) as it dies. This whole process takes maybe 4-5 seconds. After dying, it will immediately start again, which makes me think it is not a plug fouling/flooding issue.

Now the fun part, if I press the gas a little and hold it, it dies. If I press the gas and immediately release it, the rpms increase, if I repeatedly open and close the throttle it will increase rpm to about 2800, but won't go any higher. It almost acts like some engines I have worked on with clogged carb jets (using the accelerator pump to provide fuel). Obviously that's not the case here, but perhaps the power fc is using the TPS rate change to perform a similar function? My TPS values are being read correctly. My MAP is connected to the port on the firewall side of the UIM just downstream of the TB

I am at a loss to what to test next. I have a datalogit and will happily provide any setting values that anyone thinks might be pertinent. Is it possible I have a clogged injector? My PFC is not indicating knock (thankfully)

I would love to hear what the experts out there think! Thanks in advance for any tips!
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Old 07-08-18, 12:58 PM
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It occurred to me that a potential cause for my symptoms was a partially clogged injector(or two). I was able to keep it idling and running by spraying small amounts of starting fluid into the IACV port on the face of the TB. Confirming insufficient fuel, I then used fc edit to try to determine which one of my injectors was clogged. Changing the size variable to 70% for the rear injector resulted in a smooth 1000rpm idle. After 15 seconds or so it died though, with an immediate drop in rpm and no perceptible resurgence. I am thinking that the injector is clogged and the spray pattern is messed up so it's more of a drip. Perhaps I am getting enough atomization now with the longer duty cycle to make it idle, but the excess liquid fuel is causing it to foul after a bit. I think this could explain my results. I will pull the injectors and take them to a machine shop to have them cleaned/flow tested I guess.

If you are reading this and have comments or recommendations, feel free to post.

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Old 07-10-18, 12:43 PM
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Have you pressurized the system to confirm no vacuum or boost leaks?
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Old 07-11-18, 10:14 AM
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I haven't. I hadn't heard of doing that. I did just find a thread discussing how to do it though. With SD, only leaks downstream of the MAP sensor port would affect idle right? I'll check it out. I should have my injectors back later today.

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Old 07-11-18, 06:07 PM
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Remove all the injectors and have them cleaned.
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