NA6 Rough Startup idle

93_Clubman · Postby **93_Clubman** » Tue Jul 15, 2014 4:22 pm

gslender wrote:So not likely to be the problem.

I'm well aware the fuel pump was replaced, & I'm not suggesting the fuel pump is the issue. I'm suggesting it's the connectors at the inside top of the fuel gauge/pump assembly, ie the assembly that attaches to the top of the tank. This doesn't get replaced with the fuel pump, & wasn't checked as of Friday night when the OP turned his attention to the immobiliser. So still possibly the problem.

gslender · Postby **gslender** » Tue Jul 15, 2014 5:50 pm

93_Clubman wrote:fuel gauge/pump assembly, ie the assembly that attaches to the top of the tank. This doesn't get replaced with the fuel pump

True.

I guess it depends on if just the pump was replaced, or if the 2nd hand item he received was the entire assembly. When I received a 2nd hand pump for a MX5/Miata I was given the entire assembly - so I assumed the same, but yes if just pump was purchased then it would have just been without the assembly.

Even so, this job would require disconnecting the wires and connectors (freshening the connectors and scratching away carbon) and often the pump requires soldering to complete, and so that was also why I assumed this wasn't done and the entire assembly was replaced - the OP didn't seem like the type to solder up the pump unless someone else did the work (of which you'd wonder why they didn't just diagnose the problem correctly at the time!?)

I love a good mystery !

93_Clubman · Postby **93_Clubman** » Wed Jul 16, 2014 11:09 am

gslender wrote:I love a good mystery !

MX5s I've seen had push on/pull off connectors at either end of the wiring harness that runs between the top of the assembly & the fuel pump. So if pump only is replaced wiring harness remains connected at top of assembly with the plactic connector insulating blocks shielding visibility of the poor connection.

That said, this may not be the problem, which is why suggest checking for continuity at the outside top of the tank rather than opening the tank up again. Also from the suspicions the OP has there may also be another issue to do with no spark in addition to the no fuel issue.

Tumbles · Postby **Tumbles** » Sun Jul 20, 2014 12:08 am

Just to update: I've given up.

Got a friend with a trailer to tow it to a mechanic.

Will let you know how it all turns out once it's on the road again.

Tumbles · Postby **Tumbles** » Wed Jul 23, 2014 3:12 am

Mechanic:
Tidied up wiring and removed 2nd immobiliser.
Fuel Injector Relay was replaced and some stuff done in that area. From what I could make out, it was still clicking, but was warped so it wasn't making contact. Kind of awkward.

Now to update, I still have the original issue which I describe in the very first post of this thread, which is slightly longer crank times and then poor idle for about 10 seconds. See the video in my first post.

At least it starts and goes. One headache down.

Also they forgot to reconnect my inner dash light wiring so driving around tonight was severe guesstimation on speed. Frankly I was more worried about not being able to keep an eye on temp, fuel and oil pressure. Should be sorted out tomorrow.

gslender · Postby **gslender** » Wed Jul 23, 2014 7:22 am

Idle air valves. There are two... One operated by coolant temp on the top left side of the intake manifold, the other is electric and is operated by the computer/ECU located under the throttle assembly.

One of them might be sticking, not moving or opening/closing correctly.

You'll have to get someone who can inspect them to do so.

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Tumbles · Postby **Tumbles** » Thu Jul 24, 2014 1:09 am

gslender wrote:Idle air valves. There are two... One operated by coolant temp on the top left side of the intake manifold, the other is electric and is operated by the computer/ECU located under the throttle assembly.

One of them might be sticking, not moving or opening/closing correctly.

You'll have to get someone who can inspect them to do so.

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Idle air valves affect startup?

gslender · Postby **gslender** » Thu Jul 24, 2014 8:30 am

Air, fuel, spark effect everything, including startup.

Fuel is regulated by injectors and they would be consistent in their operation, whether starting, cold or running warm/hot. Unlikely to be injectors. Spark is the same as they are unlikely to have cold-start issues but operate fine when warm.

Air is the only element that is irregularly controlled and has many contributors to its volume. When starting, the air flow requirements are very different to idle and different again when going from cold-start to warm-run. We start the engine by turning the key, so the computer needs to balance and control the air needs some how by itself.

Considering the air flow must be controlled and balanced during this initial starting process, the only things controlling this are the two idle air valves. If they are not operating correct (not opening enough or too much) then the computer may not be able to compensate fuel or spark to keep the engine running smoothly, or fast enough.

Go back 15 years before the 90s we had a manual choke that did the same thing... and all it controlled was the way air was fed into the engine to assist with cold-start and cold-fast-idle.

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gslender · Postby **gslender** » Thu Jul 24, 2014 8:34 am

Note that I've also said prior that the coolant engine sensor could be the fault - if the computer thinks the temp is -15 deg or 40 deg when it isn't, this will also effect cold start and idle, by how the computer try's to control the air valves and fuel/spark etc.

Have you replaced or checked that yet?

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speed · Postby **speed** » Thu Jul 24, 2014 9:32 am

Post 16 on 10 July. I also suggested replacing the sensor. It costs $20.

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Tumbles · Postby **Tumbles** » Thu Jul 24, 2014 3:52 pm

I'll replace the sensor first then.

Out of curiousity, if it is either of the idle air valves, is it a cleaning job or a replacing job?

Tumbles · Postby **Tumbles** » Thu Jul 24, 2014 4:13 pm

Also, a big round of thanks all around. I've learned more about my car and I really appreciate it.

93_Clubman · Postby **93_Clubman** » Thu Jul 24, 2014 6:08 pm

Tumbles wrote:Out of curiousity, if it is either of the idle air valves, is it a cleaning job or a replacing job?

Could be either.

gslender · Postby **gslender** » Fri Jul 25, 2014 8:00 am

Tumbles wrote:Also, a big round of thanks all around. I've learned more about my car and I really appreciate it.

Could also be a gasket job... There is a very small thin rubber gasket that is known to perish easily on the idle valve under the throttle body. Most times it was that when the idle valve wasn't working, but I've not seen it cause startup idle issues.

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Tumbles · Postby **Tumbles** » Tue Dec 02, 2014 1:53 am

The trend I've noticed is that air temperature and humidity affect it. Starting up in rainy whether or damper weather with more moisture allows key click to start with no issues. In hotter, dryer weather, it needs to struggle for a bit before starting.

Rear coolant sensor was replaced and it hasn't changed anything.

Sorry for no updates. Life has been busy. I got the rear main leak sorted, slave cylinder changed over (the one I bought from mx5carparts.co.uk [non-genuine] broke down in less than a year, so I got one from 949Racing and it's holding up for now), also got Nitro Dann to run a direct line from master to slave and not back and forth OEM setup.

I'll be moving onto Idle Air Control as the next thing soon.