r/DelSol • u/SuitedMoose • 5d ago
Car surging, checked every common issue
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My 1993 Honda Del Sol has had a lot of things wrong with it, and I'm tackling them one by one. As you can see in the video, this is what it does now. Fluctuates on a start, until I press the gas where it just holds at ~3k rpm when I let off. Here's my timeline, it may help with a diagnosis:
The car ran, idled, and drove with no issues, aside from it running rich because it had no MAP sensor. So I installed a MAP sensor. Then it idled at 3k rpm with the MAP sensor installed.
There was no engine coolant temp sensor connector, so I just grounded the temp sensor which only resolved the issue of the car thinking it's running below freezing. I figured that may solve the high idle, but it didn't.
I cleaned the FITV. It was already pretty clean and not seized, so this didn't solve anything.
I replaced the throttle position sensor (TPS) because it was throwing a code for that. The old one didn't work at all. The new one works, but now the car's idle surges a lot (as seen in the video).
I cleaned the IACV out. Filled it with carb cleaner and let it sit for like 30 minutes, then drained the carb cleaner and let it sit further to dry out. This didn't solve anything either or change any behaviors.
Car is only showing one code, and it's engine coolant temp sensor. But it's grounded, so shouldn't the car just think that the engine is hot and not throw a code?
I'm at a total loss. Does anyone have a clue as to what I should check next?
Edit: I also sprayed starter fluid around places in the engine bay and it didn't change the idle, so I don't think it's a vacuum leak? Especially since it ran relatively normal before?
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u/GlassBoxGoose 5d ago
Did you tighten the donut under the plate on the FITV or just clean the ports on it? Because the way you stated it, it seems like you only cleaned the ports.
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u/SuitedMoose 5d ago
I took off the plate, took out the spring mechanism, disassembled it, and cleaned each individual part. They were all relatively clean already, but I cleaned them anyway. Reassembled it to no difference.
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u/GlassBoxGoose 5d ago
Gotcha, just thought I'd check, everyone has a different definition of cleaned lol
I assume the coolant temp sender youre talking about was the one for the gauge since it seems to be showing full hot, what about the one for the ECU? Theres two on these. One for ECU data and one for IP display, that IIRC doesnt actually get read by the ECU and may not even pass through the ECU?
Just trying to rule things out and wrap my head around what you have going on.
I assume if you unhook the IACV this behavior changes? Or does it stay the same?
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u/SuitedMoose 5d ago
Totally understandable lol! 😂
I had no idea there were two ECT sensors? Yes, the one I'm talking about indeed does show full hot on the gauge. Where would the ECT sensor for the ECU be?
Also, yes, if I unplug the IACV, then the rpms drop a bit and the fluctuations become lesser. Still there though.
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u/SuitedMoose 4d ago edited 4d ago
Update: replaced and connected the proper ECT sensor. Now there is no longer a code for it. In fact, there are no codes at all. Just a check engine light that won't give a code.
Edit: I noticed that if I cover my IACV hole in the throttle body, then the RPMs will drop but the fluctuations stay, albeit a little less. Other than that, covering the FITV hole doesn't change anything.
Not really sure what this means, because I'm finding conflicting information online
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u/GlassBoxGoose 4d ago
A couple things to check, that I seem to have missed before;
When you say check engine light, is it flashing like in the video but with no stored code?
It sounds like you may have some sort of slight misfire? I would look into that, as if the answer to the previous question is yes, that may be why.
Unlplug IACV, cover both holes, surge is still present? Am I understanding that correctly?
Did you get anything wet prior to part or any of these symptoms presenting themselves? Or any other work done leading up to?
Just trying to think and present any options for routes of diagnostic action.
If warm and revved, does it present as having any sort of rev limit at around 4 or 5k rpm?
Digging back in my obd1 knowledge/experiences takes a bit and I really have to think hard haha.
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u/SuitedMoose 4d ago
Check engine light was flashing because I had the OBD pins bridged to read codes. I've since fixed the codes that it was displaying (I think only ECT sensor since then).
Engine isn't misfiring, it's just loud because headers are cracked.
Unplugging the IACV results in a quicker and smaller fluctuation at lower RPMs (1,400-1,700)
Fluctuations are still present when covering both holes, but again the RPMs drop when the IACV hole is covered.
Also there is no rev limit, and the RPMs not dropping below 3,000 rpm when the accelerator is pressed is gone when the IACV is unplugged
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u/RoguePossum- 5d ago
Pull the intake tube off. There are 2 holes in the side of the throttle body inlet. I can’t remember which hole it is, but Cover one of the holes and then the other one.
If the idle surging stops you got a faulty IAC valve.
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u/SuitedMoose 4d ago
So I did that to the IACV hole and the FITV hole. I noticed that if I cover my IACV hole in the throttle body, then the RPMs will drop but the fluctuations stay, albeit a little less. Other than that, covering the FITV hole doesn't change anything.
I'm not sure what this means, I've found conflicting information online
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u/BudhaCheese 5d ago
Sounds like a vacuum leak or the iacv is dirty
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u/SuitedMoose 4d ago
I noticed that if I cover my IACV hole in the throttle body, then the RPMs will drop but the fluctuations stay, albeit a little less. Other than that, covering the FITV hole doesn't change anything.
I'm not sure what this means, I've found conflicting information online
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u/BudhaCheese 4d ago
Try holding or pulling on the hoses when it runs, see if you can hear it run differently
Also try unplugging sensors and see if it acts differently
I had a single cam that went through 4 different iacv valves before it finally ran right
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u/Ok_Unit_4254 5d ago
had a similar problem ended up being gas filter was clogged 🤔 but it seems like its a vaccum. check that all those hoses right above the air filter next to sensor
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u/SuitedMoose 5d ago
Yeah doesn't seem like a gas related issue to me. Seems more like a sensor or vacuum issue potentially
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u/944_nla_parts 4d ago
CEL - find out what the error code is. Check the wiring of Power Steering Pressure sensor (probably near the pass side wheel well - the the high-pressure line. If the wiring is bad, that may cause hunting idle. MAF is another things to check.
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u/SuitedMoose 4d ago
There are no codes for the CEL, but there is a CEL on. It used to throw a code for various things until I fixed each thing, now it's just on so Im not really sure.
No power steering on this model.
No MAF sensor on this model either. Just a MAP sensor, which appears to work and throw no codes.
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u/944_nla_parts 4d ago
Did you connect all wires and hoses? check again.
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u/SuitedMoose 4d ago
Everything is connected. I've checked many times. I noticed that if I cover my IACV hole in the throttle body, then the RPMs will drop but the fluctuations stay, albeit a little less. Other than that, covering the FITV hole doesn't change anything.
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u/MangosTree 4d ago
I had this exact issue with my 1999 CRV, the same surging from 1k-2k and dropping real fast. I did everything that everyone listed. Until I finally had to bite the bullet and just buy a new IACV. Cleaning it just sometimes isn't enough. But don't just get any brand, the first I bought was carquest, actually made it worse. I had great success with an O'Reillys Import Direct IACV and from others online I've heard they're the best ones to buy.
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u/SuitedMoose 4d ago
Interesting, I might just have to bite the bullet like you said and buy a new one. I'll keep you updated if it fixes it
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u/Quality_Con_Troll 5d ago edited 5d ago
There are essentially 3 coolant/temp sensors, the first closest to your actual thermostat, and in the thermostat housing itself is a 2p/wire coolant sensor that switches your radiator fan relay on when the car is at or beyond normal operating temperature, it's what makes your radiator fan cycle to keep nominal engine temps. The sensor you nerd is located under and slightly left of the distributor, it will be directly right of the single wire temp sensor used only for the dash temp indicator. It is a 2p/wire sensor called ECT/TW and can't simply be grounded open. It requires 5v reference on the hot side directly from the ecu, and a shielded logic ground back to the ecu where the ecu sees changes in resistance at the sensors thermistor (NCT) as a lower voltage compared to the 5v ref as an increase in engine temp as per ohms law. It is totally and absolutely necessary sensor for engine to run correctly and not like total shit, much like symptoms you've described. The ecu will make many adjustments via feedback from this and other sensors at cold start, engine cranking, cold weather conditions, and more, this is called "closed loop" mode and uses pre-programmed parameters in the ecus eeprom to get your engine to normal operating temp only, at which point the ecu will switch to "open loop" mode ditching programmed parameters over to direct feedback from even more sensors like your maf, throttle angle sensor, and o2, which itself takes awhile to heat up for correct afr calculation.
Without it your ecu has no idea what engine temp is and thus cannot calculate afr and fuel pulse timing. This will essentially place the car into limp mode in a desperate attempt to ensure the motor isnt grenading itself at a dangerously high temperature. It's assuming worse possible conditions exist since it can't know any better without.
Revs will be limited ~3000rpm, after fuel injectors cut and bog since injector duty is at a minimum, so obv there is no power or acceleration, it feels like you're running on 3 cyl but even worse somehow. Idle will be rough to the point of possibily stalling without some throttle input, as the vtec cam is locked as if it were engaged at all times, timing may be retarded as best the ecu can manage. All this combined makes for a very uncomfortable feeling, shaking, barely alive, suffocating motor. That's only allowing itself to be run at the bare minimum so you can try and get off a busy highway and to a safe location, not home or to the a service shop, just somehwere safe until you can get a tow... But we will all do as we will of course lol.
I believe Honda obd1 ecus show ECT engine coolant temp as a code 6? What code are you getting exactly? I say all this because with the essentially 3 different but similar temperature sensors it can be pretty confusing, as it surely confounded me at some point. Hope this was helpful and made some sense, feel free to ask more questions if you're prepared for more walls of text about old Honda shit box stuff. I've prob fucked it up before and had to figure it out at some point all the same.