420A [SOLVED]Horrible idle (I have searched for days)

me2151 · Mar 17, 2016

I know this account was only made a little while ago but I have been searching for days for a fix to my Idle issues. I just bought a '95 Eclipse GS(N/A) with a motor from a Talon(420A). When the car has sat overnight it will idle smooth until it warms up. Once it warms up the car idles at about 750-900 RPM but it is very rough(like its missing). At the same time as the rough idle I can hear the intake sucking increasingly more air in and then the engine starts missing more(RPMs stay about the same). It hesitates to rev until about 4k RPM, from 4k to redline is smooth but once it drops below 4k it runs rough. Another thing to note. If I try to hold the RPMs at anything under 4k despite not moving the throttle position the RPMs fluctuate(hold rev at 3k and it will slowly drop from 3k to 2.5k back up to 3k repeatedly despite not moving my foot).
The car is running VERY rich during all of this other than above 4k(Can smell fuel and lots of carbon buildup on injectors and in intake).

I have done the following:
Cleaned TB(Was filthy)
Tried different ECU(Had spare from Talon or eclipse. I don't know which. Idled good for 5 minutes then issue returned)
Replace TPS
Check spark plugs for Gap(Gapped at 0.034)
Checked wires for spark(Strong Spark)
Monitored O2 voltage(my scanner read 0.185v unless I have it gas then it dropped to 0.00v)
Replace Camshaft Position Sensor(Had CEL for)
Check Timing(Correct)
Disconnect EGR for testing(EGR good)

While it is idling rough I can disconnect the ISC,TPS AND CMP(camshaft sensor) and have NO change in idle.

The main difference that I noticed in my problem compared to everyone else or that I have not found yet is the Intake sound. It is extremely loud when its rough. I will try to get a video tomorrow.

Sometimes if its rough and I give it little jolts of throttle it will smooth out for like 5 seconds then be rough again.

gdb1039 · Mar 17, 2016

Sounds like a vacuum leak, check all your vacuum lines to be sure they are not disconnected, ripped, rotted or anything else.

me2151 · Mar 17, 2016

I knew I was forgetting something... Used 3/4 can Carb cleaner, no leaks on hoses, gaskets or Brake booster line. Or injectors. But thanks for the quick reply.

OGDSM1989 · Mar 18, 2016

Mas Air ... could be dirty as it sounds like ....

me2151 · Mar 18, 2016

I was under the impression I only have a MAP sensor not a MAS. Is is a non-turbo. Can this still cause this problem?

OGDSM1989 · Mar 18, 2016

You can check the Map ... but I am pretty sure you still have a MAS / MAF of some type, by the air filter. I would check them all ....

me2151 · Mar 18, 2016

I can confirm that there is no mas/maf on this engine. I cleaned the map sensor with no change. I have figured out the extreme intake noise is the ISC opening up trying to save the idle. I can unplug the ISC and the intake sound stays the same but idle will still try to die.

Here is the video of the idle.

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OGDSM1989 · Mar 18, 2016

Thats my fault I did not realize ( read) it was a 420a ...... and this makes complete sense out the ISC

me2151 · Mar 18, 2016

That's perfectly fine. I figured out the Intake sound was the ISC because I unplugged the ISC and the noise didn't come back but it was still struggleing with idle. Not next thing to take car of is fuel filter and injectors. The previous owner said this started a little bit after they replaced the fuel pump. I wonder if the new pump picked up some sediment and its in the injectors/ filter. Our filter is infront of the passenger rear wheel correct?

ohlegend · Mar 18, 2016

What about the Cam Sensor or Crank Sensor? From the video, it is possible that one of these sensors is on its way out.

me2151 · Mar 18, 2016

ohlegend said:
What about the Cam Sensor or Crank Sensor? From the video, it is possible that one of these sensors is on its way out.

I was receiving ECU code P1391 which is intermittent signal on CKP or CMP. I replaced the Camshaft sensor but failed to re read the codes. So the Camshaft sensor is brand new. If the crankshaft sensor is on the way out this can happen?

EDIT: I read into a back Crank position sensor and it does fit the symptoms. Can a bad CKP also cause a code for an ignition coil?

luv2rallye · Mar 19, 2016

me2151 said:
The car is running VERY rich during all of this other than above 4k(Can smell fuel and lots of carbon buildup on injectors and in intake).

Monitored O2 voltage(my scanner read 0.185v unless I have it gas then it dropped to 0.00v)

I hope the O2 voltage is not staying that low. When in closed loop, the O2 sensor should be constantly oscillating between less than 0.2v and greater than 0.7v. Less than 0.45v signals the ECU the mixture is too lean and the ECU will then try to richen the mixture (which is what you're reporting). So you may have a bad front O2 sensor which is worth checking into. Or, of course, you may have some other problem preventing closed loop mode so the ECU keeps the mixture rich.

me2151 · Mar 19, 2016

I also have a feeling the o2 sensor is going bad. Are there any free tests I can do on the o2 sensor and the crankshaft position sensor? I kinda ran out of money on this check for 2 weeks.

luv2rallye · Mar 19, 2016

O2 test: http://www.gnttype.org/techarea/ecmsensors/O2sensors.html

DBT spyder · Mar 19, 2016

Was the car ever overheated or has high miles? the reason i'm asking is because i too have a 420A powered eclipse and it did something very similar. i tried almost everything but finally the problem was found. it was a slowly leaking head gasket allowing water to leak into the cylinders and making it run like $#!&. only when the RPMs were high enough it would run smooth but at idle and lower RPMs it would barely stay running. mine was minorly overheated at one point and had about 200,000 miles on it. i suspect the slight overheating caused the head gasket to leak.

me2151 · Mar 20, 2016

Thanks for the help guys. I made it worse

I am not giving up!!!

luv2rallye said:
O2 test: http://www.gnttype.org/techarea/ecmsensors/O2sensors.html

I have found corrosion on the O2 Wires but Ill get to that in a few.

DBT spyder said:
Was the car ever overheated or has high miles? the reason i'm asking is because i too have a 420A powered eclipse and it did something very similar. i tried almost everything but finally the problem was found. it was a slowly leaking head gasket allowing water to leak into the cylinders and making it run like $#!&. only when the RPMs were high enough it would run smooth but at idle and lower RPMs it would barely stay running. mine was minorly overheated at one point and had about 200,000 miles on it. i suspect the slight overheating caused the head gasket to leak.

The engine was rebuilt 45k miles ago(top and bottom end) but has not overheated. Im not having a loss in coolant(I have indeed checked)

On to where I made it worse. So I was fiddling with some sensor wires and started the car up. after a few minutes it was still running like crap so I started to unplug sensors 1 by 1 to see if I could get any audible change. Unfortunately it put too much slack on the main harness and the harness sat on the EGR return pipe thingy(the one that goes to the intake) and melted through the insulation and possibly wires. I have taken a close look at my wires and they are oldand brittle and I would not doubt if they are causing some of my issues.
I am not able to find a proper harness in a junkyard or online. I have plenty of soldering experience and can read wiring diagrams just fine. My question is should I rewire the whole harness from ECU connector to pigtails or just patches here and there? I feel it would be more reliable if I do the whole harness. Also Does the harness go inside the cabin at all or is it another pigtail connecting that? Do keep in mind that my ECU is in the Engine bay since it is a NT.

me2151 · Mar 22, 2016

So I have a feeling it might be my timing. I checked it when I got the car but I don't think I checked it right. I have found cracks on my timing belt and It makes me feel like it may have stretched and jumped teeth. Also when I had my scanner hooked up it was saying my idle timing was between 12-17 degrees12 at first the 17 when getting crappy)

ThunderChild · Mar 22, 2016

You could try patch repairs vs tackling the whole harness right now. 90% of the wires from the ecm should go to the engine. Part of the harness go's inside to report to gauges iirc. Behind the battery through the firewall.

Patch repair while you look for a clean harness at a salvage yard. Then you could clean it up, do a tuck or whatever.

Your idle problem could be related to the CKP. it directly controls spark, and when fouled put can cause erratic timing and cause the car to die. If your belt is chewed up, I'd dig into things and to a t-belt/water pump replacement and swap in a new crank sensor as well as front o2. Get it all set up right and give her hell

Boost-Junkie · Mar 22, 2016

While monitoring your o2 voltage shoot carb spray through a vacuum line such as the brake booster hose and see if the o2 sensor will respond check the rear o2 voltage as well. Shoot consistent sprays and if your upstream hangs at low voltage .47 and below see if your rear is doing the same. If your rear is up near 1volt while your front is low still then your fuel adapting (upper o2 sensor is lazy) a lean mixture reported to the Ecu can cause the Ecu to go back in to open loop because it can't correct the fuel trims enough.

me2151 · Mar 23, 2016

Alright... took the car for a drive today and it was once again fine until the car warmed up. I was monitoring both o2 sensors and the downstream o2 is working fine. .47v idle and changes as I give it has. The upstream(one one the header) was at a constant .245v and was very slow to change at all. The only change it made was to .175v with a lot of gas.

Boost-Junkie · Mar 23, 2016

Bad o2 sensor it works great in open loop but when it gets hot and goes into closed loop fuel trims go rich drowning out your spark.

me2151 · Mar 24, 2016

WOOOO I am so happy! I unplugged the Upstream O2 sensor in and ran seafoam through the Vac line and it idles and drives perfect now!!! Next is replace spark plugs and o2 sensor. Then I need to figure out my speedometer issue(probably VSS) Then replace the transmission and fix up the body and seat. Speaking of. Anyone know how to take a seat apart? Ill check Vfaq real quick.

me2151 · Apr 8, 2016

Alright I have replaced the O2 sensor and my spark plugs and she purrs like a loud cat. Can a mod mark this thread as solved? I am unable to edit the title. Thanks for the help.

GT26 · Nov 4, 2020

Hi, I have the same problem with my eclipse. You said you put seaform in the vacuum line, which vacuum?

Zahory97EclipseGS · Oct 30, 2021

GT26 said:
Hi, I have the same problem with my eclipse. You said you put seaform in the vacuum line, which vacuum?

Hey bro did you ever figure out which vacuum hose it was?

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420A [SOLVED]Horrible idle (I have searched for days)

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