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This is a long user title
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3,213 Posts
Discussion Starter #1
Okay, I've had this problem for almost 3 years and it's time to solve it.

Here's my current setup:
1993 Manual Vehicle with 1999 Engine + 2001 pistons (running under OBD-I).

My problem:
Engine hesitates (almost wants to stall, goes at 300rpm and then comes back idling correctly) when I press the clutch pedal.

Symptoms:
-It happens mostly when the engine is cold, but also, sometimes later when it's warmed up.
-It looks like it's even worse when I press the brake pedal (could it be electrical-related?, brake light?)
-When I start the car, put it in reverse and then go backward, press clutch (and most of the time, wants to stall right here).
-If I press the gas pedal right before it's about to stall, it usually go idling fine
-I also found out that if I put the air (fans), this problem will not happen because RPM will be higher
-I *think* that when the temperature is cold it's less likely to happen than when it's humid and/or hot

Video:
Not yet...

Reward:
$75 REV9 gift card and many kind words.

Help me help ya!

:hello kitty:
 

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Murse Magnet
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7,818 Posts
I would try checking the vacuum hoses. Look for cracks. If you have a spray bottle and spray it on some lines and rpms change then you need a new line.
 

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Garage Quinn Motors - GQM
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2,847 Posts
1. Check compression on the engine and check for endplay on the crank. Use a pry bar on the crank pulley to push it back and have someone depress the clutch while you measure endplay. If you see movement, your thrust washers are going.

2. Check voltage off of alternator and battery.

3. Check and make sure no grounds are worn, broken, or disconnected. It wouldn't hurt to try adding additional grounds also.

Is your car running a stock ECU or an aftermarket? Still running a MAF?
 

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This is a long user title
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3,213 Posts
Discussion Starter #6

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This is a long user title
Joined
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3,213 Posts
Discussion Starter #7
I would try checking the vacuum hoses. Look for cracks. If you have a spray bottle and spray it on some lines and rpms change then you need a new line.
Will try that.
 

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This is a long user title
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3,213 Posts
Discussion Starter #8
1. Check compression on the engine and check for endplay on the crank. Use a pry bar on the crank pulley to push it back and have someone depress the clutch while you measure endplay. If you see movement, your thrust washers are going.

2. Check voltage off of alternator and battery.

3. Check and make sure no grounds are worn, broken, or disconnected. It wouldn't hurt to try adding additional grounds also.

Is your car running a stock ECU or an aftermarket? Still running a MAF?
Compression test was done earlier, 185 on all cylinders.

Alternator is still the stock one that came with my 1.6 engine, battery is new. I've had an alternator test in the past and they told me it was still fine. Could check voltage again...

For grounds, I really am not good with these. Where (from/to) is an easy spot to add some ?

Car is running stock 1.6L ECU and 1.6L AFM.
 

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Registered
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453 Posts
I know it's probably not the solution, but you could try adjusting your idle using the diagnostics port, no?

Also, I had just replaced my alternator because I had a similar issue and I have a 90, 1.6. So it seems that it may be that. I'd double check the alternator and check all the connections to the battery. Try running the car at idle and use electronics to see if it bogs down. Like signals, brights, heat etc. See if they give you any difference.

If not, it may be more internal. But whomever above suggested a vacuum leak, that'd be my next place to look.
 

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Miata Master
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2,138 Posts
Its the common 1.8 swap idle dip. The 1.6 electronics are too primitive to run the 1.8 well. The its either your IAC is bad. Since it only happens when its cold. Unplug the IAC and see if the issue changes. If it doesn't change the IAC is bad. If not you will need to manually adjust your idle with the set screw on the trhottle body. My car ran the exact same way. Thats why I switched to a 1.8 harness and electronics. Remedied the problem.
 

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453 Posts
A lot of people have a wiring harness for sale on the forums. I may even have one for sale if you need. I only got it because I needed a replacement negative terminal wire from the battery to the chasis. If you need it, let me know. I have no use for it. I can give you pics as well.

I believe there are two wiring harnesses, I may not have the one you need, it's from the battery to the fuse box.

Also, the wiring harness did not have a slot for the pigtail for the hartop, so it may be a 1.6. Thus, ignore this post, sorry I can't help you out.
 

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Registered
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11,685 Posts
Clutch had nothing too do with the ECU... Well, very little anyway. There is a switch that the pedal actuates, but that's it.

My guess: throw out bearing and/or pilot bearing. The throw out is causing some binding, especially when things are cold. That causes the droop. It's worse when hitting the brake due to the vacuum booster not having much to work with. Crack open the trans case and check both bearings.

I would also check and maybe replace the IAC valve. It should be increasing idle to compensate for these things and obviously isn't.
 

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Miata Master
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2,138 Posts
Maybe a simple and off base answer, but maybe the O2 sensor is bad/fouled? Only $25 to swap in. I had a cold hesitation/misfire and did this on my 1.6 and the car works well now.

The car should still be running a single wire 02. Doubt it would cause the issue.
 
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