93 240sx dies on deceleration

[djsilver]

93 240sx, base model, 5-speed, 197k miles, cylinder compression within FSM specs.

I have a Factory Service Manual but no ready access to a Consult toolI've check the ecu and currently have no hard faults

The idle is normally stable at 750-800 rpm when warm, w/o A/C running.When driving the car, the idle will fall below 500rpm when decelerating and will frequently stall. If it doesn't stall, the IACV/AAC will eventually regulate the idle back to 750-800. This problem only happens when driving the vehicle. I can't replicate the problem in the driveway. I've tried revving it and I've tried running it at 2-3000rpm then releasing but it decelerates and idles just fine. I've also tried the same experiment while holding the brakes to see if the brake booster may be involved (no change).

The IACV-air regulator (bypass) works properly to increase cold idle, then closes when warm.

The IACV-FICD solenoid increases idle to about 1200 when I turn on the A/C but the IACV-AAC will cut back the idle to about 850-900 after a few seconds.

The power steering pressure switch functions correctly, increasing the idle when turning the steering wheel at idle.

The FSM describes a Vacuum Control Valve in the IAA Idle Adjusting Unit. The description is vague but it sounds like a mechanical vacuum relief valve. I could use a vacuum gauge to test it but I can't find any documentation on its release setting. I suspect that if this vacuum relief were stuck closed it could be causing the problem but I'm looking for guidance.

[s13sr20chris]

off the top of my head i cant think of any vacuum control valve in the iaa circuit. see if you can get her to stumble, then whack iaa and see if she perks back up. those motors get old you know.

[AZhitman]

I'm thinking more along the lines of the swirl-control butterflies int he manifold. They're actuated by a vacuum-controlled actuator on the back of the manifold (has a rod sticking up out of it)...

Clean your intake mani and check the vacuum line to the bottom of that actuator.

[nuknght]

i used to have that prob w/ my 91 ka24de, the car would die because of the vaccum line on thefire wall. the one that runs from the intake manifold to the brake booster. I ended up removing the bracket that held it to the firewall and it solved the problem.....too much tension on the line when the engine revved

[downbyfive]

93 240sx, base model, 5-speed, 197k miles, cylinder compression within FSM specs.

I have a Factory Service Manual but no ready access to a Consult toolI've check the ecu and currently have no hard faults

The idle is normally stable at 750-800 rpm when warm, w/o A/C running.When driving the car, the idle will fall below 500rpm when decelerating and will frequently stall. If it doesn't stall, the IACV/AAC will eventually regulate the idle back to 750-800. This problem only happens when driving the vehicle. I can't replicate the problem in the driveway. I've tried revving it and I've tried running it at 2-3000rpm then releasing but it decelerates and idles just fine. I've also tried the same experiment while holding the brakes to see if the brake booster may be involved (no change).

The IACV-air regulator (bypass) works properly to increase cold idle, then closes when warm.

The IACV-FICD solenoid increases idle to about 1200 when I turn on the A/C but the IACV-AAC will cut back the idle to about 850-900 after a few seconds.

The power steering pressure switch functions correctly, increasing the idle when turning the steering wheel at idle.

The FSM describes a Vacuum Control Valve in the IAA Idle Adjusting Unit. The description is vague but it sounds like a mechanical vacuum relief valve. I could use a vacuum gauge to test it but I can't find any documentation on its release setting. I suspect that if this vacuum relief were stuck closed it could be causing the problem but I'm looking for guidance.

my car has also developed the exact same problem as of late....did you end up finding a solution? was it the vacuum line? it's totally driving me nuts, as I take the DC Beltway to work every day, and traffic is constantly rapidly accelerating and decelerating and I have to watch to make sure my car doesn't stall out while avoiding traffic....it's no fun....

[downbyfive]

well, I checked the bracket holding the vacuum line and I'm confident that isn't the problem...anyone else have any ideas?

[stratmatt777]

And now I will bump a THREE year old post! See I am using the search function as everyone asks us newbies with questions to!

Anyone know how to fix this problem?

I read some of the threads on the cars that wont start so you guys don't have to repeat yourselves over and over! I bought this car in 2002 with 54,000 miles on it. It now has 112,000. -It has been making the "marbles in a can" noise that I read about on here probably for months but I coudn't afford to have it fixed. -When I take it out of gear on the freeway exit ramp, if the lights are on, it often drops to 300rpms and almost dies or does die. The more electrical accs running the more likely it dies. I put it in gear to restart it and then have to catch it and give it gas before it dies while pulling up to the stop sign. The rest of the way home I notice that the headlights dim ever-so-slightly when I apply brakes (brake lights using power, I guess). The car has a 90's era Viper alarm but I've never had a problem with it.

About a week ago I tried to start it and it sounded normal for the first two truns- like it was gonna start maybe- but then it didn't. It just turns over and nothing happens. I replaced the spark plugs and observed spark from plug #1. The old plug's threads were wet and smelled of fuel.

I called a mechanic and told him about the "marbles in a can sound" and he said that my engine may be destroyed. He said to stick my finger in a spark plug hole and crank it- if my finger is blown out from the compression the engine is not destroyed from bad valve timing. It passed this test.

The air filter is pretty new. So the dieing/electrical problems probably indicate an alternator problem? Several months ago when I replaced the bad starter I hooked my batt up to AAA's tester and it said that my batt and alternator were both in excellent condition (maybe the tow truck driver misread the tester machine?).

I have never replaced the oxygen sensor in 50,000 miles- that wouldn't cause this would it (I have one I'll install tomorrow)?

To troubleshoot this thing tomorrow I'm going to do the following things that I've read about in a couple threads here:Check for tear in hose on valve coverCheck groundsCheck fusesCheck fuel line pressure/filter/priming with key in run pos.I should replace the cap, rotor and wires for routine maintenance since I have not done anything routine like that in 50,000 miles due to lake of $.Is replacing the coil routine maintenance at 112,000?

What are all the things I should replace for routine maintenance?All filters everywhere I suppose?

How do you check fuel injectors (when do they wear out)?

I do have a DMM and understand how electricity works in general (simple V=IR knowledge).

I saw qat727 mentioned jumped timing. How does that happen? Maybe it happened to my car with a failing timing chain tensioner?

One thing is for sure- I am having the timing chain replaced on Monday so that I my engine doesn't self-destruct (assuming it hasn't already). The mechanic I calle dsaid that timing chain engines are not non-interference engines (which seems like a really stupid design decision to someone who doesn't know everything about car engines).

Alternator?

The PCV valve has never been replaced either. All that's ever been done is oil and filter, brakes, air filter, a thermostat, a starter 5 months ago, and I just did the plugs.